Maturity is the best thing you can convey. To that end, it will benefit you to appear to have (and to have) your own things going on: ask questions that will tell you how to accomplish your future goals. For instance, if you're a programmer and you're interested in startups, ask about entrepreneurship on campus, on-campus attitudes around that, etc. Similarly, do not ask how you can best prepare for college -- college isn't/shouldn't be a destination.