The assumption that your teen years are the best, more shining and radiant part of your life—and that as soon as you reach legal majority you become a decaying thing that can only crawl in the rotting morass of adulthood all the way to your death—is very much a common Japanese idea... but it isn't at all a Western idea; more like the opposite, in fact. I'm surprised nobody felt offended by this strip and reacted with anger.
I guess we've all already been mentally colonized by the Japanese. :P Come to think of it, I haven't read any rants against lolicon manga in a long time...
Why would we feel offended?
They call "decaying" people of thirty something. It's a pretty strong word.
I know right? The cult of childhood and teenhood in Japan is simply baffling to Occidentals. Especially in Protestant countries: it goes against the whole tradition of Reformed Christianity. Japan is the only country in the world were a woman of 25 is a decrepit old-timer no man would pay attention to.
If you look closely, Catholics aren't really better. Catholic tradition since the Middle Ages is that children (at least under seven but could be older too) are angels of purity that must be protected from carnal depravity. Calvinist tradition (think New England at the time of the Salem witch trials) is that children are corrupt things that must be exorcised through discipline and punishment, kind of like how Carrie's mom raised Carrie. None of them cares about the Kinsey reports and what they taught us about child sexuality. It's not easy to find a religious type who accepts the sexuality of children as a healthy and natural thing.
Somehow the Japanese, even though most of them haven't read Kinsey, have a better understanding of these things. The naughty lolis of Itou Hachi are more like real children than anything you find in American tv.
At least when it comes to post-puberty teens the mainstream media in the West seem to have accepted the notion that they are sexual in nature, as seen in most teen shows and movies... although anything beyond kisses and petting is cast in a darker light. I think the only genre where teen sex happens consistently and is presented in an unjudging way is the horror genre... too bad the slasher always comes and kills them in the middle of it, lmao.