Um first of all where do you all live???? I am in canada and your 12 to work at A&W and it's any day... They don't really care as long as your working.
Its normally 15 for Saturday jobs and 16 for full time jobs if you have left school if you were stopping on to 6th form then it would have to be just a Saturday and holidays job
In MI its 16 to start in a restaurant job, although I have know some people who waitressed at 15.