Science shows there’s underlying variability in sleep demands and these change based on age but people can also get used to less sleep even though they benefit from more.

In general newborns sleep 12-16 hours per day but not continuously. Age 6-12 average 9-12 hours. Teens average 8-10 hours. Between 25 and 64 most people are 7 to 9 hours which is where the 8 hours comes from. Seniors sleep less and rarely continuously through the night.

Talking about averages always excludes outliers. Some people are 6’6” and others 4’8, but odds are you’re still capable of sleeping more with better habits. There’s methods to learn how to fall asleep more easily and huge benefits from consistent sleep patterns. Further, it can make a huge difference what your room is like, lower temperatures and a lack of light is almost universally beneficial.

I think it’s pretty commonly recognized that different people have different sleep duration requirements (within reason). The 8 hour rule is a popular rule of thumb, but in no way does current sleep science say that’s a hard rule that is true for everyone.