He has a point - this is the second post you've made like this. There's nothing wrong with thinking about what you'd like to do, but speaking from experience, that may change 10 times in the next couple of years. I would concentrate on doing as well as you can in school, having extra-curricular activities, and just being successful now. Concentrate on what will make you the best student you can be, and then you'll be able to get into multiple schools when the time comes, regardless of what you want to do. Also, your high school should have a guidance department, and guidance counselors are very knowledgeable about what it takes to get into colleges, what you should focus on, etc.
One other thing to think about - for certain majors or careers, the school you choose might be of the utmost importance. This is really not true for most careers or schools. People think if they don't go to Harvard or Yale or someplace like that, they're a failure. Education is what you make of it. Companies have enough sense to look at what you can do, and how well you can do it. I've read a lot of articles about this, since I have a high-schooler also, and what I've read indicates individual capabilities are just as important as the college you went to.
As an example, I have a friend whose son went to college last year. He is brilliant in science, and is only the second person in our state to achieve 7 perfect scores on the Advanced Placement exams (the maximum you could get). He also was close to perfect SAT scores. He opted for a smaller college in Ohio, because he didn't want to be just another smart kid at Brown or Yale or the other schools he was accepted at; at his college, he's basically the star science student after his first year, and has full run of the science labs. He'll get tremendous recommendations from his professors for grad school, and probably opportunities he wouldn't get elsewhere.