Gary Marcus tackles the question in his new book Guitar Zero: The New Musician and the Science of Learning. Marcus summarizes his thesis in an interview:
I think the former paradigm was that you really had to learn a skill early. And it's still probably better to learn it early. But you don't have to give up hope if you want to continue learning… Some of best studies are by Eric Knudsen at Stanford. He showed adult barn owls could do similar things as young owls if they learned them incrementally. Another study showed that the older owls could do just as well in a real-world context if there were predators around. The way I interpret these studies is that incentive and motivation are critical.
Maria Popova has more.
The Dish 