N.B.
I hate to say this, but...you just have to ride it out. My son has ALWAYS been an early riser and it was until he was about 1 1/2 that he started sleeping (regularly) until 6am. Now at 26 months it is pretty unusual for him to get up before 6am -- most times it is closer to 6:30-7am.
"Back in the day" we tried putting him to bed earlier and it NEVER helped. It just made bedtime a little more challenging. When he reached 22 months, or so, we adjusted his bedtime back to 8pm -- we start his stories at 7:30pm so he is in bed between 7:45-8pm. But I can't say this helped anything other than a less challenging bedtime.
Good luck!