Good luck to your son! I’ve attached an undergraduate rocket engineering competition event that might be of interest to your student. I have also attached a list of 2022 participants. He will see that he can be involved in some great rocket projects at many universities. This year, Australian teams took the win!
My advice is for him to apply as the major that most excites him as he will have a greater chance of putting a strong application together that way. Aerospace is generally a smaller department at most universities and seems to be very close knit. As with many engineering degrees, having a degree in aerospace doesn’t mean only working in aerospace, just as you can work in aerospace without an aerospace degree. One of my friends is an aerospace undergrad and works in biomechanics/robotics. Friends of my husband’s that are aerospace engineers from Southern California work as imagineers (I think that’s what it’s called) for Disney. Good luck and I hope he ends up in a great place for him!!!