For the first half of my life I could sleep till noon if you let me and happily stay up till 3am reading or geeking out on something. In college I once accidentally slept through dinner.
All that changed in the last decade or so. Some combination of age and perhaps too much time working with people three, eight, twelve hours ahead. Now I get tired by 10pm and wake up most days around 5am.
I’ve stopped trying to fight it and just accept that might quiet time is now when I wake, as the sun is rising, and this quiet time is often my only chance to sit and think and, ideally, write a bit before the swirl of time catches me again.