K.P.
We go through this every day too! My son is 1 and wakes up b/w 5 and 5:30 each morning. We tried pushing his bedtime back, but then he just woke-up cranky at 5:00. A couple of days ago, we shortened the bedtime routine and extended the night by 30 minutes and we have had a "sleeper" until 6. It could be a fluke, but I have my fingers crossed.
Essentially, his internal clock is what it is, but we found that if he played his little tush off right until bedtime, he was physically more tired and is sleeping longer. Instead of 3 books, we read 1 when we get home and 2 before bed. Instead of eating at 5:30, we eat at 6. We pushed the entire night back.
We also put a few soft toys in his crib. It seemed like he was waking-up at 5:00, but wasn't really ready to get up and moving until 6:00. I put a couple of snugglies in there, so if he gets up early, he can cuddle and lay back down. So far, so good.
Good luck!