My first suggestion is to work in the industry. Yes college is helpful but most of the radio people I know don't have degrees. The ones that do aren't always broadcast or communications majors. For every broadcast major, I know 2 who majored in something else.
That said, go to college and major in communications, journalism, something like that. I'd suggest he start making contacts now. Radio stations are always looking for promo kids, interns, whatever. Take ANY job, paid or unpaid he can get at a radio or TV station. Learn everything. I strongly recommend going to a University with a radio and TV station. Absolutely work at both if he can handle it.
The more actual work you do in the industry the better. No one wants a kid with a Radio/TV degree who's never worked at a station.
Radio is a grunt work business unless you are at the Stern, Rush, Seacrest level. Djs run their own boards, the are expected to help with production, some have producers to help them gather their info but they are also expected to bring their own material to the table.
Radio news people, think of stories, track down leads and run all over town. They are expected to be journalists as well as talking heads. There are very few radio news people who show up and read what's given to them.
I haven't done a lot of TV work but I've worked closely with several TV stations. A lot of TV news people are expected to file their own stories and they've even been known to act as their own camera person on occasion.
I know a lot of the 'hosts' on TV started in TV news and while they seemingly popped up out of nowhere, they likely paid their dues somewhere.
He should also know that it is a cut-throat business. Talent jobs are hard to get and hard to keep. There isn't much job security.
I'm not saying for 1 second that he shouldn't go for it. I just like to point out some realities that a lot of HS and even college students haven't realized yet. I know at 17/18 I didn't have a clue. He sounds like a very smart and hard working young man, that will take him far in this business.
In radio talent is important, but who you know is also important. It is a very small industry.
There is nothing wrong with experimenting in both radio and TV in college. He might find he prefers one to the other.
Also don't discount the behind the scenes jobs. I think most people who go into radio, start by wanting to be the star, but I've seen so many talented people get passion about programming, production, and producing that they realize that being on air isn't always the be-all, end all.
If he has any questions feel free to ask.