On either saturday and/or sunday I'll let myself sleep until I wake up (usually 12noon-2pm). I'm fortunate enough that my first morning meeting is 9:30, and it takes about half an hour commute. My alarm starts at 7:15, and I usually snooze until around 8... it takes me nearly an hour to get going once up, and even then, I'm usually walking in the door just as standup is starting.
I'm amazed by the early-start types, as I've tried... It only made me really tired and funny for a few days, then increasingly grumpy. At 19, I worked two jobs, first at 4:30am, and second ending around midnight... I was a really grumpy young man by the end of that month (quit one of the jobs, just couldn't keep up with both).
Then I managed to find a job doing creatives/design, and fell into programming from that. All the same, in a lot of places "office hours" have been the biggest contention in the workplace for me. I get things done, I have high quality output, and significantly so.
I've found that if there are no major artificial light sources, and if I've been outdoors active all day, I tend to want to fall asleep soon as its dark. And I wake up way earlier, soon as the daylight starts to hit the tent.
Maybe it's natural for /you/ to get up that early, but it never was for me (the closest I came was waking up super early for reruns of Mr. Wizard, then falling back asleep).
Works for adults, too (especially if you also reduce use of artificial lighting) though it can be a struggle to fit that into modern life—especially in the Winter, since kids don't do much running around at school these days and it's dark shortly after they get home.
As a parent, I can state that getting lots of exercise is very useful in persuading kids to go to sleep at a reasonable hour. It's not bad for the parents, either.
And it doesn't even do a good job at that either! Most public school start (830am) after parents leave for work and finish (3pm) well before parent's get off work to pick them or be home. Sure there are after school programs to cover it a bit but overall it's a pretty crappy schedule for a publicly funded babysitter.