Several months ago, in an interview with Radio Times, he said
Fast forward to a few months later. While discussing when he would be coming to America, in a brief interview with VH1, he said,“When I finish [Doctor Who], I’ll be…” before checking himself and continuing, “Well, I don’t know how old I’ll be, but by the end of next year I’ll be 29 so…”
As much as it saddens me to see a Doctor leave, it is the nature of the show and it happens. As much as I would love to see Matt Smith stay in the show for a while, I am interested to see what direction the show takes when the next Doctor is introduced."I've got another year with Doctor Who, then I will come over [to America] and give it a shot"