I can't give you a definitive answer since that's yours to make. I can tell from my experience of being in 2 startups that the team should be your most important consideration. Your product and market can and will change more often than the entire team would. You shouldn't go in feeling uncertain about the people you're working with, because its not like you can A/B Test your way out to a better situation like you can with a product/market. Sometimes, however, the opportunity can be such that you just have to play the cards you get and take a chance.

If you're main issue is compensation, then negotiate back a number that will make you comfortable without being unreasonable; it seems like you're pretty valuable to them.

Youth and startup experience shouldn't be a concern if you think their smart, dedicated and have some gusto.