Started at 15 @ DQ (had paper route, though from like 9-12 yrs old).  Worked ever since with only a break in HS during sports season, in which I worked weekends.  My senior year I decided to forego sports to work and pay for a car.   When I went to trade school, I worked a 40+ hour work week and went to school.  I'd literally change into my work shirt while driving to work.  I got out of school at 3 and was supposed to be to work at 3.  I was usually there by 3:10.
So, I see both sides.  Yes, I did miss out on a lot of things.  I wish I'd played football and gone out for track my senior year, but oh well.  On the flipside, I believe those work experiences prepared me and molded my work ethic that I have now...  If I had to give advice to someone in HS, I'd advise them not to work except in the summer.