My DS is like that. He always has been, since he was a baby. Everybody would tell me to just put him to bed later, and then he'd sleep later, but it doesn't work. He once stayed up until 1 am, on New Year's, and STILL was up by 5:45, and was hell on wheels for three days afterwards. If I try to ignore him and go back to sleep, he climbs on my head and pulls on my ears and screams in my ear and generally drives me bonkers until I wake up with him. I think some kids are really just "programmed" to be early risers, unfortunately. That said, there are ways to cope, and to edge them into sleeping a bit later.
Have you tried a blackout curtain? My kids have, behind the shades in their room, a thick heavy black curtain that blocks out every speck of light. That's helped us a lot. It also helps to keep them in the dark until roughly the hour when you'd LIKE them to get up, even if it means sitting in a darkened room for a few hours after waking. Also, if you can get away with it, you might try not feeding him until a more ideal waking time. The idea is that our bodies become naturally cued to wake up at a certain time if we're generally exposed to daylight and fed at that time.
If he's willing to entertain himself once he wakes, you could try confining him in a safe place, and letting him play with toys or even (heresy, I know!) watch TV until you wake. I didn't notice how old you said he was-- is he young enough for something like a pack-and-play or crib-- you could set him in there and go back to bed.
Doing these things, I did manage to convince DS to sleep until 6. Then I had to meet him halfway by moving my own accustomed bedtime to earlier, so that I could be functional for him once he did wake.
The good news is though that when he turned 3, and could start to understand a little better, I was able to teach him to stay in his bed until I came to get him, and now I leave him with a pile of books and a few toys and a cup of water next to his bed, and he most days can manage to entertain himself until even as late as 7. So I think it does get better as they get older, because even if they're awake early, they don't need you as much.