My boys wake up early too (they are 2 and 4 years old) and there is nothing that I can do about it. I've tried putting them to bed early and late. I've tried moving their nap schedule around and I've tried eliminating their nap. Nothing has worked. They are just early risers. I finally decided that if they wake up before 5 am, it's still night time and they have to go back to bed. But 5 am is the start of the day - for them. I turn on a one-hour show, set them up on the couch with bowls of dry cheerios, and go back to bed until 6 am. (This is easier with a 4 year old than a 2 year old, I know).
I also worried about preschool, but my early-rising, nap refusing 4 year old did just fine. Once preschool started I was able to put him to bed earlier because he was so tired at night. I would have preferred him to sleep in rather than go to bed early, but his body never slept in. I'm betting that your son won't always wake up as early as 5 am, but he might just be an early-rising kid. I'd put him to bed at his normal bed time and let him get up at 5 am.
I know it's so hard, but it won't last forever. Good luck to you.