Math seems to becoming less of a young man's game. There is simply to much to learn now before you reach a field still ripe with unsolved problems. There still lots of said problems, they are just built on top of other things.
However, I don't see that math is really all that important for 99% of web 2.0 startups.
Anyway, older people bring critical skills to a startup such as creativity, which can improve over time as you try and observe all sorts of ideas.
But this sort of proves the original point. Since cs/programming has lower barriers to entry (cool new stuff is still "easy") there are many more opportunities for young people.
[1] http://www.cs.utexas.edu/users/EWD/transcriptions/EWD10xx/EWD1036.html