I have never been one to lie-in, even in my younger days. as soon as I wake up I get out of bed, usually by 07.30 but prefer before 07.00. I find that if I stay in bed any longer it makes feel tired and lazy for the rest of the day. I never set an alarm clock as I don't start work until 14.00hrs and I rarely go to bed before midnight.
I also see it as a waste of time when I could be up and out and doing something interesting.
I work with a lot of youngsters, mostly between 20 and 35 and you can tell the ones that have spent the whole morning in bed as they usually come to work looking tired and worn out, the ones that get up earlier are usually bright and refreshed. Its not because they have been out late or gone to bed late, they have spent a long time in bed, whats it all about?
I go to bed at 11 through week take a while to drop off and ake up at 8 and am usually knackered. At weekends I sit up till early hours then wake up about 8 and am fine
I need at least 7 hours, preferably 8 but then will sleep for 10 hours-ish on a Saturday night/Sunday morning, although until I was about 20/21 on Sundays I would sleep until 11/12 most weeks, if I do that now I get a headache! Apparently teenagers do need lots more sleep than people expect though which can be 'made up' at weekends with long lie ins, wouldn't account for the 20-35 year olds though!