Our ped. said 3 is the national average these days, which surprised me. My son will be 3 the beginning of April and he has sort of been potty training himself, which I didn't expect. However, not completely. Try a video. Potty Power is pretty good, actually. I got it on Amazon. Also, you really do have to let them run around with nothing on for most of the days you're home with him. It really helps them recognize the signals. When we began doing this with our son, and he'd ask for a diaper, we'd say "it's time to use your potty now! You don't need a diaper!" and we'd take him in the bathroom and sit him down.
Personally, I don't see the value of pull ups and think this was another way for the diaper companies to make more money. In a kid's mind, they are no different than diapers because they can go to the bathroom in them, so big deal? That whole pull them up like they're underwear? Why not just use underwear? And as for using them at night, again, what's the difference between that and a diaper except less absorbency and more mess for you to clean up? Save your money and just buy underwear. I've talked to moms who have actually thought pull ups hindered success and cause confusion. It's an extra step in an already multi-step process and who needs that??
Good luck! I know how hard it is!