Sorry I don't have much, was just wondering how you treat it when he wakes up? 4.30am is still sleep time, so if DS woke I would sit in his room in the dark, feed & not stir up, then cuddle & back into bed. We would treat it like any other wake up, until around 6ish...then ok we are up.
Could just be a bad pattern he has gotten into, most babies need at leat 10-12 hrs sleep at night & esp at that age. So I wouldn't think he was really ready at that time IYKWIM. Is it long before he then wants to be back asleep?
Unfortunately with lots of babies a later bed doesn't always mean a later wake up. 7pm is very reasonable at that age I would stick with that & just try & extend the sleep time.
Sorry I don't think I've offered much help.