Fun fact: if you, as an adult, tell miserable children that their youth is the best that life will ever be, and that it’s all just downhill from there, there’s a percentage of them who will hear this and think “well, I guess I better kill myself before that happens.” And a certain percentage of those will proceed to do that and succeed.
Anyway what I’m saying is that any time you feel tempted to say that, you should instead consider shutting the fuck up. Just because you peaked at 16 doesn’t mean anyone else did. Most peoples’ lives get better than that.