Maybe you wouldn't call it bootstrapping, but someone whose in their mid 20s, who has been working as an engineer for startups for the past 5 years, could easily have saved $25,000-$75,000. IF you live cheaply and "bootstrap" by focusing on your startup %100 of the time and funding it from these savings you could easily have a 2 year runway there... assuming also that your co-founders have similar savings.

This is pretty much what I did, I saved money and now don't have to worry about contracts or client work, I can focus solely on the company and keep costs down as if I had taken outside investment.