You are in a somewhat unique position due to your age. There are many 'age compliance' shops for those between 17-25 (with 17 year olds often needing to have a parent sign up because 17 in some areas is 'too young to contract with'). These usually are checking to make sure you are carded for movies or game purchases you might be too young for or for purchase of cigarettes or alcohol you may be too young for.
Nationwide Services Group standardly offers restaurant dining for up to 2 people, where one must be between 21 and 25 and purchase alcohol. (NOTE the requirement is attempt to purchase. If you don't drink you are not required to drink it, only to purchase it.)
New Image Marketing offers tobacco compliance at convenience stores. I believe Corporate Research International does so as well.
For other, non age-restrictive work, Market Force International (blue portal) offers jobs in virtually every city, town and crossroads in the country. The same holds true at present for one of the clients of Bare International and a few clients of Corporate Research International.
Normally I encourage folks to start with Corporate Research because they generally offer the best shop training (but the lowest paying shops) to get your feet wet. Like anything else, this field has some jargon, but once you have the hang of it they all pretty much use the same terminology.