Why does my 16 week old wake up at 5am no matter what?

I've tried putting him to bed a bit earlier around 6:30pm and a bit later around 7:30pm, but he still wakes up at 5am. He usually wakes up just one time per night for a full feed and straight back to sleep, but it could be anywhere from 12am to 4am and then up for the day at 5am.

I'd really like him to sleep at least until 6/6:30am so I have time to get up, ready for work, and get our toddler ready for the day.

Any ideas?