C.D.
My son did this when he was small, and now his own daughter does this - has since she was born (she's six). I said to him, "Welcome to my world." No matter how late we put her to bed, she gets up at the same time. The only thing that seems to happen with a later bedtime is that she's still up at 5:15, but spends the day sleep deprived.
Is it possible that he's hungry,wet or both?
I think body clocks are pretty much individual.
Believe it or not, time will fly by, and all too soon you'll be able to sleep as late as you want to ... because he'll be grown.
:^)
Best of luck, and try to enjoy these years.
C.