What does an intern in a hospital do and how old do you have to be to be one?

An intern takes care of patients, runs tests, that sort of thing. Surgical interns do some operations. The big thing with interns is that they can't do any of this unsupervised. They always need a resident or attending watching them.

Regarding age, there's no SET age, but you need to complete College and Medical School, so that's 8 years right there. Plus, lets say, K-8 grade is another 8 years, so 16 years so far. Plus 4 years of highschool, you'd need to be at least 25. (Assuming you started Kindergarten at 5.)