Based on a poll that purely collected people's opinions and has no scientific backing whatsoever but I'm going to cite it anyway, you get your best sleep at age 24. Then it all goes downhill from there.
Yeah, of course you get your best sleep in your early 20s. You don't have to worry if sleeping in just slightly the wrong position will render one of your limbs useless for a month. Remember when we were kids and could fall 10 feet from a tree and just shake it off? We've really let ourselves go since then. Gotta get in that 8 year old shape again. Back when we didn't know things and were invincible. Now we know too much and our bones hurt if the weather is bad.