Trouble sleeping? It might be biology - Mayo Clinic Press

Sleep schedules often change with age. That’s why teens are known for sleeping until noon, while retirees often wake up before the sun.
If you’re getting tired earlier than you want to be, you may be able to blame biology.
Circadian rhythm is the natural process bodies use to control the timing of functions like sleep and appetite. Work schedules, exposure to light and other environmental factors influence this internal sleep clock.
Your circadian rhythm is also responsible for age-related sleep changes. Check out how it affects different age groups and what you can do about it.