My son is 15 mnths old & wants to go to bed at 6:15 & wakes every morning at 5. Any ideas?No light in room?

We put a dark navy flannel curtain over his one window. He naps fine in there & always puts himself to sleep. How do we get him to go to bed later? When we put him down later, it makes no diff. He wakes up even earlier. HELP!!!!!!