J.S.
My daughter is 2 years 6 months and we've been through some nap issues recently too. I agree with several of the posts who said that they get overtired easily, making is much harder to sleep (counterintuitive).
I am absolutely positive my little one needs her naps, no matter what my mother in law says! ANyway, we often have "lunch" around 10:30 or 11 at the latest - I've found that these days she has to be in to nap by 11:30 at the latest or we've missed her "sleep window" and she'll not fall asleep. Every day is a little different - it depends on what time she gets up etc - if she wakes up super early she might be in for her nap by 11 or even before. ANd some days she can make it til 12 but not usually.
If all this gets messed up and we miss her sleep window and she's in her crib taking an playing but not sleeping, my back up plan is always the stroller. If she's not asleep by 2 she goes for a walk in the stroller and will fall right asleep and stay asleep until you stop walking. And an hr or an hr and a half is MUCH better than nothing for her so I do it when necessary.
I do try to have her in her crib ready for bedtime by 7:30 everynight but lately she's been battlign me there and often I am in her room with her until9pm before she fals asleep. But then she sleeps til 7 or 8am and we start all over!
Bottom line - my advice is try an earlier lunch and nap, and put him in even if he doesn't nap right now because it could pass and soon enough he'll be sleeping like he used to.
good luck
ps I put my little girl in at 11:30 today and I think I missed her sleep window - it's 12 and she's not asleep yet : (