Age... Does it Matter?

When is a good time to start interning? I use to think you had to wait til you were atleast a junior in college. And that it was really hard to get an internship as well. In reality, you can start applying as early as 18 years old. It may be harder to get the job, but I interned with one girl that had just graduated from high school. Granted, she interned during May, which is oftentimes a transition period between the spring and summer interns.
Some magazines offer internships to high school students. I've heard of some magazines that offer one week internship opportunities for high schoolers through school charity auctions. I've only seen them in the northeast because the schools are close to NYC, but there may be some at local magazines elsewhere.
But what's the average age of interns? Most are a junior or senior in college, or even a recent graduate!