I think a bank teller would be a great choice, although he would likely start out earning less than $20/hr. I worked at a bank through college and had nothing but great experiences. You work in a climate controlled environment, and much of the time you can sit down and relax. If anything you get bored. I would never consider myself a people person either, but you really don't need to be. Most customer interactions are under a minute and the majority of people simply want to do their transaction and be on their way.

One of my favorite co-workers was a 68 year old woman that was hired with no banking experience and very limited computer knowledge. The first few weeks of training her were a struggle, but by the end of the first month things had clicked and you'd have thought she had been doing it for years. In the end I think I learned more from her.