I fall asleep around 2-3am every night and am up at 7:15am during the week. I'm 39. I've been a night owl since I was a teen, and even today I have to force myself to sleep. During vacations it becomes extreme, I easily stay up till 6-7am and sleep till 12 or so - which seems to be ideal as I always revert to those times given 3-4 days where I'm not required to be up early. Adjusting my schedule back to "normal" involves skipping sleep for a night.

I've noticed the same thing. In my twenties waking up before ten was extremely difficult and made getting into work stressful every morning. But now in my thirties I find myself awake when the sun rises without issue.

My lights are out at 11, but getting up at 7 is difficult still. On the other hand, it was straight impossible to do at 25.