[amk]

There are several reasons. Depending on the startup, it may be one or more of these:

* Older and more experienced programmers may need a bigger salary, which startups cannot always afford.

* Older and more experienced programmers may be more suited to work in larger organisations with set procedures and practices, which is not suited for startups.

* Older programmers have other commitments which may prevent them from putting more energy in the startup. It may also be more of a risk (money wise) for them to join a startup which may or may not succeed.