You guys are thinking like adults?

I'm 42, married, own a house, and paid off vehicles. I'll tell you when I find out.

“A new ‘big data’ study shows precisely when executive function matures.”

just in time to join the world of executive dysfunction …

Analysis of the data revealed that performance on almost all the tasks improved with age, with the biggest improvements occurring between early to middle adolescence (10-15 years of age), and smaller but still significant improvements from middle to late adolescence (15-18 years). Performance on all the measures stabilized to adult levels between 18 and 20 years of age.

About 5 months into being in their graves.

I mean, some adults in their 40s seem to think like adolescents and teenagers, so maybe never...

There's a point where you reach peak mental state and then begins to decline due to senescence. Senescence itself is considered to begin during adulthood, around your 20s. Afterwards, it's really a tradeoff of what you and your life experiences do to stave it off. Trying to avoid being overweight, drug abuse, and other negative health habits can lower the rate at which senescence occurs, while trying to feed your mind and body with engaging and challenging activities that can help improve them will also help you stimulate and increase your mental faculties, increasing the cap senescence needs to reach before it catches up. Like the article says, your mind can still keep on changing well into your thirties, but there's no fixed age, rather, you determine it

/me Ctrl+F Piaget (no results)

Anyway. ~15yo seems sensible acc. to Piaget's theory of child development. But I think that we should take it with a grain of salt, for the reasons people here are highlighting - your development never truly stops, a 20yo adult won't think like a 40yo and neither will like a 80yo. Our experiences shape it a lot, it isn't just physiological.