That 8 hours is ball park. Diff age has diff pattern and depend on your own body

For example when you are young u sleep longer and as you age u dont need much sleep. These days i sleep 12am and autowake up at 6am and feel fresh. When in my teens sleep 12 am wake up 8 or 9 am sometime 10am

The quality of sleep also is important
If you have light sleep vs deep sleep u gonna feel tired. Dont eat too near to bed time ( give 2 to 3 hours)

These days i am lucky that as soon as i see the clock hit 12am, my body power down. If i dont see the clock then i can pass til 1 or 2. Not sure why but it makes it easier