Depends what age we are talking about and it varies by individual of course. Generally, we need more sleep as children than as adults. Think about it, the younger we are the more our cells are growing and dividing and multiplying, and sleep is a restorative time for us. Women during pregnancy also usually require more sleep. My sleep needs became less when I got into my 40’s, but also my sleep is more broken, before that age I almost never woke in the middle of the night, but I also have thyroid problems now, which sort of artificially affect my sleep.
I think the averages are something like 11–12 hours for older infants and toddlers, with the majority of sleep at night, but with naps during the day. Grade school we need 9–10. Teens need 9–11. Adults 7–9. I was a perfect 9 hour sleeper most of my life. If I was shorted sleep, I eventually made it up that day with a nap or within a few days, and it always worked out to 9 hours, until my 40’s as I mentioned. Sleep tends to be in 1.5 hour cycles, literally if I nap it is usually for 1.5 or 3 hours. 9 obviously a multiple of that sort of cycle. But, now I often only get 7–8 and don’t need to nap to get the full 9 that I used to.