Has anyone heard of "theoretical mathematical physicist"?

A theoretical physicist is someone who models systems and does a lot of math and computer work. They typically have a PhD in physics. It's not a major or really even a job title, it just sounds like your son put a bunch of impressive-sounding words together and said 'I want to be that'. A physics major is a good place to start. Princeton is a great school for physics, but it's grad program is better - and you won't do a bachelors and a PhD at the same school. It's considered bad form.