DS1 has always been a terrible sleeper.
DS2 & DD are younger and both sleep better.
No matter what time we put them to bed (usually 6 but we've tried earlier and later) he's up before dawn everyday.
He dropped his naps at 16months.
It doesn't make a difference if we have a 'quite' day or a busy day, but he takes longer to get to sleep after a quiet one.
He shares a room with DS2 and is waking him up, ds2 is 20m old and loves his sleep. Poor thing is ratty by 9 every day. Can't have him in with us (no room for his bed) and they love sharing a room together.
I've removed most of the toys so there's nothing massively stimulating but he's got a great imagination so is never bored!
What can I try?