How late can someone start chess and yet still scale the peaks? It does help to start early as chess skill is more easily acquired by the young. Though there are examples of some very late starters such as Joseph Henry Blackburne.
Blackburne played checkers as a child but switched to chess at the age of 18. Nonetheless he became one of the most successful players of his day, making a living as a chess professional and winning a host of tournaments.
Wilhelm Steinitz was very impressed with this game in which Blackburne allowed Black to win a kingside pawn and then generated a devastating attack along the open files: