Realistic, yes. But is it realistic to think you'll get paid a salary worth mentioning? Not so much.
It sounds like you want to get in on something early, and most things early just don't have much money in them. My advice: find a start up you love and go for it. If you're really gung ho about a specific startup and are willing to share the founders' vision, I have a hard time believing they would reject you're help. Expecting a decent salary though, is probably too much.
I was in the same situation as you 2 months ago. I couldn't find a startup I loved so I started my own. Now, I'm developing a product out of my old bedroom in my parents house (free housing ftw). When the product's done, I'll move out west.
The one thing I would stress is to always have a backup plan. Things will not go according to plan as much as you'd like, so be ready. I'm living with my parents now, but if they kick me out I know exactly where else I can get free/cheap housing while I develop. If I run out of money and realize my startup won't make it, I can most likely go back to school. If I can't get back in school, I know I would have an absolute blast being a bartender on a cruise ship. After I save up some money I'll start over.