Teens as young as 13 can sign up with survey companies to answer questions and make their own cash. I don't have a 13-year-old in the house, yet, but it won't be long. I've been compiling this list of sites my daughter can use to make money when she gets to that age. (She already works for these sites for kids.)
Of course I'm not going to recommend any site for my daughter that doesn't treat me well when I take their surveys, or isn't highly recommended. So here is a list of a few good survey sites that pay teenagers:
GlobalTestMarket - Minimum age 14. GTM is a global company, so teenagers worldwide should have no trouble with this one.
Swagbucks - Minimum age is 13. I'm not sure if they're global, but I know they do have programs in several areas of the world. They're well work checking out.
MySurvey - Minimum age 14 in most countries. Their $10 redemption level doesn't take that long to reach. You can cash out for paypal.
SurveySavvy - Minimum age 14, worldwide. They'll send a check any time you choose to cash out. If you refer people, you earn incentives for the surveys they take, as well.
American Consumer Opinion Panel - Despite the "American" in their name, this company accepts everyone 14 and older, worldwide. They pay by check or paypal.
e-Poll - ePoll is USA only, but takes panelists as young as 13-years-old.
TeensEyes is a site for U.S. teenagers ages 13-18.
PanelPolls.com - PanelPolls actually takes kids from ages 6 to 17, so any U.S. teenagers ages 13-17 can sign up for this one. My kids love surveys from this site - they're often about new tv shows, and pay more generously than most sites do. In addition to surveys, you can get in on mobile app and beta game testing or online communities which often pay bonuses of $10. If you get into the online focus groups or game testing projects you may earn bonuses of $35 or more.
If you have experience with an awesome site I haven't listed, feel free to share in the comments. Spam will not be approved, though, so please tell us something helpful about the site if you drop a link. Thanks!