A similar question was discussed some time ago over at http://quomodocumque.wordpress.com/2009/01/21/claimed-proof-of-the-abc-conjecture/#comment-3179. There it was pointed out that William H. Young (of, say, Hausdorff-Young fame) didn't publish much before 40. After 40 he had a successful career, with a prolific publication record. This said, it is reportedit is reported that he was a very talented student.