I think there is no age limit in learning. You can start to learn anything at anytime in your life. If you insist on learning you`ll learn it.
Learning anything new means facing difficulties that can last sometime weeks. I remember having spent a week to resolve one simple thing in asp.net. I get discouraged, but I didn`t listen to my feelings, I just listened my wish to learn. And finally i resolved it. Hopefully we live in a world where internet resolve all your problems. Especially the forums are good for resolving almost anything.

There is no limit in human brain until you fly away of this world. See the extrordinary example of Stephen Hawking. I think this tells all. Good luck!