Youth is what seems so prized, that today, so many people--who can no longer make any claim to youth--wish to continue looking young and put themselves through so much, to achieve that end. But I am guessing that even those who want to look young, won't really want to go back to their youth. Whenever I think about it, I am quite glad I am no longer a teenager, especially in today's world, where anything deemed as weakness can be exposed and ripped apart cruelly, not just by your own circle, but by the world at large. When one is young, one is so conscious of one's shortfalls,plus the need to impress the world around is so great. The angst of the young can be so torturous. It's good to grow out of that.
Now youthfulness is another thing altogether. To me it signifies someone with the mental/physical energy of youth, but without the angst, someone who has gained wisdom from all the experiences they have been through and still have enthusiasm for life. I have a much older cousin like that, still ready--at 83--to have fun, and it's not that she's a super healthy 80 year old either.
Yesterdays are what those folks, not in their youth, have plenty of. My yesterdays form a kaleidoscope of colour, some blue, some really dark, dark and some bright and rainbow-like.
Yawn, sleepy time -- "Yawn, yawn , yawn your sleepies out (3)
And wiggle your waggles away. " A verse from a song my junior school kids sing :-)