Why do old people generally wake up relatively early every morning, even when they have reason to be up early, while most young people will sleep in late, sometimes very late, if they have no other plans?
What is the biological change that occurs in humans as we age that prevents us from sleeping in?
Thanks.
The older you get, the less sleep you generally need. If an older person goes to bed at a reasonable time, then, they wake up pretty early in the morning.
Your question should therefore be, “What biological change occurs in humans as we age that make us not require as much sleep?”
The less time you spend sleeping, the more time there is to be crotchety.
They only get up early if they go to bed early. My family is a family of night owls. I think the earliest my dad ever got up once he quit working was 7 AM. He’d go to bed at midnight or later.
Heck, I graduated college 6 years ago, and my bedtime’s gone from 1-2 AM to 10-11 PM.
Old people tend to go to bed much earlier than young folk. Early to bed and early to rise.
Got to pee.
Tris
Plus you gotta get up and go pee. Several times a night. After the second or third time at night, you figure you might as well stay up and get a head start on the day’s grumpings.
I imagine a lifetime of training has a lot to do with it. My father-in-law wakes every morning at seven AM because, he says, that’s the time he always had to get up to go to work and he just can’t seem to snap himself out of that pattren.
I sleep late, you little whippersnapper.
I think they do it just to piss us baby-boomers off. We only have a limited amount of time to get our cars fixed or go to the license branch or the doctor’s office to not take time off work. Who do we see there taking up valuable prime time? The Old Farts.
…makes you old.
It may be due to reduced melatonin levels. This is a site/cite I found in a search that mentions it.
They don’t?
Grandma has gone from getting out of bed 9ish to doing it around noon. Then she has breakfast, which Gramps has left prepared c. 8am before going back to lie down in bed. After having breakfast, she prepares lunch and they eat c. 1pm. They have dinner c.8pm. He goes to sleep around 10pm; she around 3am.
Maybe she’s waking up early relative to the next day.
Gramps, Middlebro and myself have always been “early in, early out.” We take his sudden love of the bed as proof that Gramps won’t last much (in his case, it may mean another couple years). Grandma, Mom and Lilbro have always been laters.
Hell, who knows what time those pesky neighborhood kids will start scampering about, getting on your lawn. Someone has to be there on alert, ready to wave a cane in the air. 
…and your gal goes out with other guys.
Do you have a cite for this? That’s fascinating if it’s true. I’m interested in this because I feel like I sleep a bit more than I’d like to (9-10 hours a day) but if I forcibly wake myself up I feel cranky and just end up taking a nap later. That would seem like an actual benefit to aging.
Although (warning: welcome to Anecdote Land) my grandmother was an extreme night owl. She would always stay up until 3, 4AM or later and get up 12 noon / 1PM-ish. I guess I inherited something from her, because those are more or less the hours I keep (luckily for me, I work nights).
Hell, the older you get, the less time you have left. Why waste any of it sleeping? Sleep’s overrated anyway. 
I think it starts with the advent of babies in the household, so you start going to bed just after them in order to get as much sleep as possible before THEY wake up at sparrows fart.
And after a while the habit sticks, even when they are older and sleeping in until after noon and you have to kick them in the ribs to wake them.
It’s also (in my case still) the chance to get some ‘alone time’ in the house before they all get up and moving for school or work or whatever. I personally treasure those hours between 5.30 and 7.00 am. It’s sheer bliss watching the sun come up before the kids do.
And sometimes I need to pee as well. 
Old fart here. I go to bed at around 11:00 PM usually. Lately I’ve been waking up and getting out of bed around 4:00 to 4:30 AM. I’ve always been an early riser but what I’m doing now is ridiculous. Maybe older people realize they are running out of time; maybe we get up early in order to see more of one of the relatively few days we have left.