[gjenkin]

pg wrote this essay some time ago: http://www.paulgraham.com/start.html

He discusses the elements you need to create a successful startup. To answer your question of "when" to start a startup, it may be worth considering these elements. When you have them (or 2 out of 3 of them since the third element is to spend as little money as possible, and you can't really do that until you're in it) it may be time.

Another relevant pg essay: http://www.paulgraham.com/notnot.html

Here he discusses some of the dimensions you include in your question (age, wealth, in/out of college) and analyses their impact on one's decision to start (or not start) a startup.