As I tend to do around here, here's something nobody has mentioned: It might just be who he is.
Of my kids, 3 of them (20, 18, 10) are normal. My 8 is a morning person. Regardless of bedtime, like staying up late on Friday watchin movies, he's up at 6:30 on Saturday. He also sleeps the heaviest and is easiest to wake up on school days.
Conversely, his 6yo sister is a night person. She will lay in her bed singing quietly (not every night) till 11 even on a school night. Even on nights when they're in bed on time and she's asleep by 10, she's the hardest to wake up at 7:30 on weekdays.
It's really hard to do anything more disciplinary with her as she's doing everything ok . . . general evening routine, routine bedtime, routine get ready actions. Then she's in bed, in the dark (shades down but there's some outside light), leaving her sleeping sister alone, not playing with toys, minding her own business.
Anyway, the point is that it may just be his personality. It's possible, that you'll never "break" him of it, but you should absolutely establish routine and time-based boundaries. At some point, as long as he's within the established parameters, you may just have to let him be him.