Is he able to realize that he has to go...is he dry through the night, and or get up and go if he has to?
My DS3 could have stopped wearing them last December. He has been dry through the night since then. We were too chicken to stop putting him in them that early. We waited until he was wearing underwear all day (that was about May). Once he was able to realize, on his own, that he had to go to the bathroom, and either went on his own, or told us he had to go and was able to wait long enough to get to a bathroom (sometime that was 10 - 15 minutes, depending on where we were at...driving and all) that was the end of all pull-ups, day and night. I just couldn't see spending money on them when he wasn't wearing them during the day, and was completely dry at night for the past several months! Since we stopped using them, he has had only one "accident". It was at night, and he was really sick and out of it because of medication, and just didn't realize he had to go. But other than that, he will actually wake up in the middle of the night and go all by himself, if he has to go...now if only we can convince him to tuck himself back in without waking us up to do so!!!
If he is dry through the night, I would say give it a shot. Get one of those platic matress protectors to put on under the sheets, that way, if he has an accident, the matress will be protected. Good luck!