If not in school, then find one of the local programming/hacker clubs around your community and hang out there. After getting to know some of the members, you might be able to work something out like trading some beers/coffees for their time. It's hard to give specifics to how to find a mentor, but patience and an understanding of how to relate concepts to someone learning are the key for anyone teaching.
I found from mentoring friends a few years younger than me in school that it not only improved their own programming skills, but mine as well. Mainly because it makes you rethink how you interpret concepts so you can relate them to someone who doesn't understand them as well yet (which is also a useful skill when talking to clients or bosses that aren't developers). Sometimes you also learn something new (as no university covers 100% exactly the same material, though most are generally similar). I have a saying that if one cannot explain a concept to someone who is genuinely interested with sufficient time, then one does not really know the topic as well as they think.