That is a good point. Off the top of my head, at 25 you should move, while at 35 connections might be enough to compensate for the difference between, say, Boston and SV.
I'm 37. I have set up businesses in London, Houston, Chicago, NYC, Edinburgh and (soon) Sydney. You can hook into a city in just a couple of months, being from elsewhere sometimes helps in creating interest, and the people who will be of most use to you in a start-up are likely to be very open to new people if they've got the skills, drive and charisma needed to succeed. Just my 2c.
I dunno.. even in biotech startups tend to cluster around specific areas (and universities).. A lot of state govts want to attract business, but have yet to achieve critical mass.
Without a doubt, you have to be near a university.
