L.A.
Looks like you have some good advice already. Put some safe toys in the crib (soft books, small cuddlies, etc.), make sure there is a "room darkening" quality of shade over the window, and make sure he is well fed when he goes to bed, and that he is warm enough. 5 am is just about when a house hits its coldest phase, and kids tend to wriggle around and kick all the blankies off. And as one of the mom's said, don't rush in there and he may fall back to sleep. Being a "morning person" is one thing, but 5 am is a little too early. Unless you're a farmer or a garbage collector.
The other thing to consider is that there may be something or someone waking him up. Birds, another family member who leaves early, a cat crying to go out, etc. Even a noisy home furnace kicking on can do it.