20-somethings start companies which serve 20-something customers (Facebook, Snapchat, etc).
30-somethings start companies which serve 30-something customers, or enterprise customers of the type they've worked at (where purchasing decisions are made by 30-something directors).
There are exceptions to those rules, but they're pretty consistent.
What's important is that entrepreneurs be consistently visible across age/race/gender/class/origin/etc demographics, so all markets are best served.
When I was in college I help found to startups that focused on college market. When I graduated I focused on markets relevant to my employer. Now that my first born child is coming in focusing on parents and kids. I focus on things that solve my problems, and try to make some money on the side too.
30-somethings start companies which serve 30-something customers, or enterprise customers of the type they've worked at (where purchasing decisions are made by 30-something directors).
There are exceptions to those rules, but they're pretty consistent.
What's important is that entrepreneurs be consistently visible across age/race/gender/class/origin/etc demographics, so all markets are best served.