part time startups are harder for people that have other commitments, like a family to feed, wife or gf, busy career. That is why most of the startups are started by young single men who don't have a family they are obiligated too, a gf or wife that needs attention that takes away time from working on your startup, or people that are higher up in the food chain at corporations, which requires time as well. Furthermore, younger people can take risks because they have more time to recover from a failure.