A good thing to know is that a lot of people who work in aerospace did not major in aero specifically. There are many who majored in something like mechanical or electrical. So even if he’s set on aero as a career, you can definitely get there with a more general degree. In my opinion, when in doubt, go with the more fundamental degree as opposed to a specialized degree. But many people are thrilled with their specialized degree too.
One good tool is to go to linkedin and see who is working in a variety of positions that might be of interest and see what they majored in and where. You might be surprised at the variety you find.
Most schools offer some sort of exploratory first year within engineering, whether that’s formalized as a program or not. It can be called “first-year engineering”, “exploratory engineering”, “engineering undeclared”. That was important to my kid who didn’t know what discipline he wanted but was pretty sold on engineering in general. Only a couple of his schools required you to apply to a specific engineering major but all of the ones like that on his list were flexible in reality. One was RHIT, but they said not to worry and that it would be trivial to change his major: he applied to mechanical there, since that’s kind of generic.
However, at a minority of schools it can be difficult or impossible to change into certain major (sometimes large competitive publics). You’ll have to find out each school’s approach.
I agree with trying out a summer engineering camp. My kid did RHIT Catapult (Purdue STEP was cancelled due to covid), and it was very helpful. He picked a coding project on purpose and learned that, while he enjoyed coding, he did not want a computer-focused major.
The youtube videos can be helpful for learning about the different disciplines and what they actually do. Looking at course requirements can be helpful to see how much math, physics, whatever they’ll be taking for different majors.
All engineering degrees have high median salaries, but some jobs are more plentiful (e.g., more demand for civil compared to aero). Salary differences aren’t usually big enough to justify picking a major that you’re not super interested in. Once my son narrowed it down to mechanical, civil, electrical, chem, or biomed, he decided he just really liked chem/bio stuff. He thought electrical would frustrate him. To choose between chem and biomed, he learned from reading online that the chem degree was more versatile and had more career prospects. Realizing that he could still work in biomed with a ChemE degree helped him with his final decision, and he’s been very happy studying ChemE.
So use a lot of different information sources to narrow it down, and don’t stress too much about it. While it’s possible he may need to decide on an exact major before applying at a small minority of schools, most schools don’t require that and in fact some mandate an exploratory first year. He may also get into a major and change his mind, which is okay too.