We know that more than half of Americans are married or are living with or dating their future partner by 30. We know that the brain caps off its second and last growth spurt in your 20s as it rewires itself for adulthood, which means that whatever it is you want to change about yourself, now is the time to change it, We know that personality changes more during your 20s than at any other time in life, and we know that female fertility peaks at age 28, and things get tricky after age 35. So your 20s are the time to educate yourself about your body and your options. So when we think about child development, we all know that the first five years are a critical period for language and attachment in the brain. It's a time when your ordinary, day-to-day life has an inordinate impact on who you will become. But what we hear less about is that there's such a thing as adult development, and our 20s are that critical period of adult development. But this isn't what twenty somethings are hearing, Newspapers talk about the changing timetable of adulthood, Researchers call the 20s an extended adolescence. Journalists coin silly nick names for twenty somethings like "twixters"and "kidults." It's true! As a culture, we have trivialized what is actually the defining decade of adulthood.