Age DOES matter, but like I said, if you are relevant, then it doesn't. If you are 40 and trying to come in the music business then you can forget it.
Too Short, E-40, Ice T, Ice Cube, Dr. Dre and many others are well into their 30's (and one in their 40's) and they still matter.
In that respect, age doesn't matter if you still got something to contribute.
Peace.