I’m 64 and would give anything to be able to sleep at least 8 hours a night. I have to get up at 4am for work every weekday so my normal is about 6 hours of sleep a night as there is too much going on at home with my elderly in-laws medical situations for me to go to bed before 10pm. On weekends I can’t sleep past 5am, no matter what time I go to bed. I’m tired!
The body/mind can adjust to shorter sleep periods. What it cannot tolerate is no sleep.