Our Brains Don’t Fully Develop Until We’re 25. What Does That Mean For Age Gap Relationships?

"John Mayer could legally drink by the time Kiernan Shipka was born." This was one of hundreds of tweets that dominated feeds at the start of November when news emerged that the then-22-year-old Mad Men actress was seen getting dinner with the 45-year-old musician. There's no proof that the pair are dating (fans have since shared photos of Kiernan’s rumored boyfriend) but the mere idea of their partnership provoked strong reactions online.

Though the existence of romantic relationships with large age gaps is nothing new, in recent years the online critique has become louder. Lately, this critique has taken a scientific approach. These days, when rumors emerge of a new relationship with a big age gap, internet users are questioning why older people would want to date someone whose brain isn’t fully formed.

This statement is based on the notion that a person's prefrontal cortex (the part of your brain that does the decision-making) doesn't reach its final form until you turn 25. As this fact spread across social media, it became irrevocably attached to people’s disapproval of relationships with large age gaps. Most recently, this conversation included 20-year-old musician Billie Eilish after she was spotted with 31-year-old musician Jesse Rutherford, with Twitter comments calling out Rutherford for wanting a girlfriend with an undeveloped brain. 

It's not just people on the outside taking a closer look at age-gap relationships. Singer Demi Lovato's latest single, "29," is rumored to be about her past relationship with Wilmer Valderrama, which took place when she was 17 and he was 29. See also Taylor Swift, whose fans claim she wrote her new album Midnights about her romantic ties to John Mayer when she was 19 and he was 32. Taylor's recent re-release "All Too Well" also supposedly unpacks her relationship with Jake Gyllenhaal, which happened when she was 20 and the actor was 29. 

For all the recent examples, the age-gap conversation is most famously associated with Leonardo DiCaprio. In August this year, following his breakup with model and actress Camila Morrone a few months after her 25th birthday, a graph went viral on social media highlighting the fact that every single one of the 48-year-old's ex-girlfriends has been 25 or under. Recently the actor has been rumored to be dating 27-year-old Gigi Hadid.

Just how solid is the actual science behind the internet's claim that people under 25 are still waiting for their brain to develop fully? And what does it mean for age-gap relationships?

"It’s totally, totally robust," says neuroscientist Dr. Tara Swart, who has been teaching lessons on the subject for nearly 10 years. "The brain is still actively growing and changing until we are about 25," she explains. "We used to think that by the time you physically stopped growing — around the age of 18 — that your brain showed how you're going to be for the rest of your adult life, but then more recently we've seen that it still changes a lot up until the age of 25."

According to a 2013 study on brain maturation by the Saint James School of Medicine, "it is well established that the brain undergoes a rewiring process that is not complete until approximately 25 years of age." The study explains that as the brain matures, the amount of myelin increases in the brain's frontal lobes. More myelin means better neurocircuitry, allowing for a superior flow of information between brain regions. This specifically impacts things like impulse control, problem-solving, and the ability to balance short-term rewards with long-term goals. "The prefrontal cortex, the rational part of our brain, is one of the last regions of the brain to reach maturation, which explains much of the behavioral immaturity so often associated with adolescents," says psychotherapist Helen Burke-Smith, who was not involved in the study.

So what are the emotional differences between someone with a fully matured brain and someone whose brain is still in the growing stage? "[Fully matured] adults can utilize the prefrontal cortex, the brain's rational part, which helps us to respond to situations with good judgment and an awareness of long-term consequences, whereas adolescents process information utilizing the amygdala, the emotional part [of the brain]," says Burke-Smith. This means that adolescents are more likely to seek out emotional experiences, even if they are potentially threatening, she continues. Younger people are "less able to rationalize or recognize the danger in the same way adults [do]."

According to relationship counselor and BACP-accredited therapist Victoria Jeffries, the lack of prefrontal cortex development in people under the age of 25 could have significant implications as they formulate relationships. Trusting your intuition, she says, is more complicated when you're under 25. "That niggling feeling you have when something doesn't feel right is less likely to be apparent." 

If we accept the science, then two adolescents forming a relationship with each other is one thing, but it’s a different kettle of fish when one partner in the relationship is significantly older. "As valuable functions such as insight, morality, and intuition are governed by the prefrontal cortex, it could be said that a younger partner [under the age of 25] may be particularly impressionable," explains Jeffries.

The consequences of this will vary. There is no one-size-fits-all set of guidelines. It does not mean that every older person seeking a relationship with an under-25 person is a predator. It also does not mean that everyone under-25 person is unable to trust their own judgment when it comes to choosing a partner. However, Jeffries warns, "It could be that the younger partner is less likely to adequately identify what behavior or actions that their partner is displaying feels truly right or wrong, possibly exposing them to manipulation and an overall imbalance of power dynamics within the relationship."

Younger people whose decision-making part of the brain is yet to develop may be more likely to look to others for guidance as opposed to standing firmly with their own opinion. "Those with an older partner may have the tendency of following the partner's lead without weighing what is best for them. This may result in the younger of the two not fully acknowledging or identifying their own needs and best interests," says Jeffries.

Although the raw science shows that brains under the age of 25 are still developing due to physiology, Dr. Swart says that environmental factors can also impact a person's maturation level and this shouldn't be dismissed. "Up until the age of 25, a lot of people are now still living at home and are still financially dependent on their parents. So what happens out in the world actually matches up to what the brain scanning technology shows." In other words, we might put science at the crux of age-gap arguments, but lack of life experience (or indeed the opposite) is equally important to consider.

Other lifestyle factors can affect the process, too. "It's not just age, it depends on genetics, how you were brought up, your sort of personality style, and how much expressed emotion there was in your family," explains Dr. Swart.

"In general, your ability to control your impulses, your ability to judge risk and make decisions, where the prefrontal cortex is balancing the emotional systems of the brain, is less formed below the age of 25 than above the age of 25."

So, understanding that both physical and environmental factors have a huge effect on maturation, does this mean that under-25s should never date people older than them? No. Jeffries believes that every age-gap relationship is individual and should be treated on a case-by-case basis. "While age-gap relationships are by no means necessarily a bad idea," she explains, "it's important to acknowledge that there are significant differences and challenges that the couple may face."

The key, then, for any adolescent building a relationship with an older partner, is to understand the importance of establishing a healthy dynamic that works for both parties. "There is no hierarchy in a relationship, even if there is a considerable age gap," says Jeffries. "Remind yourself that simply because one of you is senior, does not make them more knowledgeable or superior. Similarly, just because your partner may be younger than you, it does not mean that they have a lesser understanding of life. Neither of you should silence your voice or ignore your own needs." 

Most importantly, a healthy dynamic needs both partners to have a sense of independence. Burke-Smith notes that a large proportion of identity development in adolescents happens through interacting with peers. "Generally, if someone is in a relationship with an older partner at this developmental time, research suggests peer relations are prioritized less, which can detrimentally impact an adolescent's crucial steps towards independence, their place within society, and who they are," she explains.

With this in mind, is there any way to address the difference in needs between partners? "Have your own interests and maintain these. This includes spending time with people your own age and maintaining the interests that you had prior to meeting your partner," says Jeffries. "You are different people with different interests and it's important to acknowledge this."