I think there has been a noticeable (not necessarily linear) paradigm shift in the treatment of adolescents and young 20-somethings in popular entertainment from the 50s to today, shifting from the simplicity of Andy Hardy, Dobie Gillis, and Gidget to the angst of Rebel Without a Cause and Easy Rider (although those guys didn't seem particularly young...) to the unearned faux sophistication and jadedness of Sixteen Candles, Buffy, Juno and their ilk.
And the age of the midlife crisis seems to have lowered as well, from the 40s or 50s (as it was usually portrayed mid-20th-century) to the mid-20s/early 30s often now.
Perhaps it was once thought that you had to have more life experience under your belt before you were dramatically interesting? Imagine a version of FOLLIES with a group of 25-year-olds revisiting the high school where they had performed and had dreams that didn't come true. Some would love that, others would roll their eyes. Both would be valid responses.