Which UM?
Purdue has a competitive secondary admission process to get into engineering majors after entering as a first year pre engineering student. This is less desirable than a school where entry just requires passing the prerequisites. A school that gives direct admission is also preferable, unless he is likely to change his major to another one that us capacity limited. If he is admitted to the school but not the major, check how difficult it will be to get into the major.
Aerospace engineering may have more limited job prospects than mechanical engineering from where one can seek aerospace jobs but also be better considered for other jobs.