The only thing I know to suggest, aside from looking for signs of being tired initially, is to set up a night-time routine.
It's gotten to the point where both my kids now ask to "go upstairs" - that's our first step in "winding down" for the evening...making sure we know where everybody's buddie's (teddy bear's), blankets, and pajamas are, and going upstairs. We'll watch a little TV, have a little water to drink, talk about the day, relax, have potty time last before going to their bedroom, and settling into bed.
Whatever your routine is, start it at the same time every night before he gets tired - maybe 40 minutes after dinner. Be diligent with it, and then he'll start to know what to expect, and will start looking forward to it.
It can be whatever you want - start with a bath, maybe rub some of the "bedtime lavendar lotion" Johnson&Johnson makes, then into pajamas, read a book, have a night-time bottle and go to bed - whatever, as long as the time is peaceful, soothing, and conducive to him winding down. Also, have a humidifier in his room or some sort of fan on low to create some "white noise". There's a humidifier walgreen's (it's a private-label sunbeam humidifier) has that has a nightlite that shines through the tank - bright enough to see in the room, but not bright enough to keep anybody awake.
just a few thoughts - for what it's worth, and good luck!