Will he ever be underwear boy?

Before Harrison's big third birthday he promised us that after the big day he'd begin using the toilet. This was completely unprompted. He had this idea himself. Pretty exciting, huh? So the day came and went and nothing. He refuses to use it. I wouldn't push him if I didn't think he was ready but he clearly knows when he has to go to the bathroom. He loves to be naked and he'll run around for a long time but when he has to pee he asks for his diaper to be put on. What?? He went pee in the toilet once... back in November! So at his three year check-up this week his pediatrician said to put all potty things away and stop talking about it for a month. Then try again. By then it should be warmer (remember, we live in Seattle..) and we can just let him go without a diaper or put on underwear and see what happens (outside - no pee on my new carpet please!) It will be pretty exciting when he does lose the diapers though - look how cute he is in underwear!