I'm 19 & I've been a catering vollie on the last 2 Great Vics, and last year my sister came with me, she was 17. Catering is good, coz you get to meet almost everyone when you're serving or barcoding or in the food courts. Its a good way to meet people. Also you finish by 8:30 usually so you can enjoy the night stuff, and sleep during the day.
Whatever you choose, its just fun to meet all the people.
Only problem with been young, is that you can't get into the pubs or buy drinks from the Cafe.
Good luck whatever you choose