I had an internship at HP when I was 16. I probably wasn't particularly useful, but I learned a lot about how the corporate world works. I'm glad I didn't have to wait until I was 18 to figure that out, and get on the right course for my education and career.

One of my high-school friends went to college for a teaching credential, only to learn at the end that he didn't like teaching.

College or not, it's extremely useful to be exposed to a field of work for at least a few months, before dedicating years if your life to it.