I don't think it's ever too late to start. Most kids seem to go through phases where you catch lots of wees (and even some poos), and then as they get older, it all seems to go out the window. I don't know why this happens, but it happened to us, and from what I hear, it seems to be a pretty common occurence... So I say stay with it. This phase is just temporary. He will go back on the potty soon, so I would recommend that you persist, but don't stress out too much. Ultimately a week or two of "failed" days, is nothing in the long run...