Yeah I should have qualified that... it's not even math or music, but rather particular subfields and a particular kind of person. 26 is too young too; I was taking that random number from the OP.

Galenson claims there is a human dimorphism between people (or at least artists) who peak young and old (summarized here: http://www.wired.com/wired/archive/14.07/genius.html)

Math, music, and chess do have the most child prodigies. It doesn't mean the converse is true, that older people are worse at them :)