If he does want to do composition he can do a BA at almost any college or university, without auditioning. He can also apply to conservatories or schools of music attached to colleges/universities for a BM in music and do composition without auditioning on an instrument. If, however, he wants to audition he certainly can.
A BA is 1/4-1/3 music and includes theory, aural skills, music history, composition ethnomusicology, technology etc. Sometimes there is a composition strand or credit for performance components.
A BM in a conservatory or school of music, whether freestanding or part of a college, is 2/3-3/4 music with the other 1/4 gen eds and some electives.
He can also major in anything at college and still take music classes and composition lessons.
Students attending grad school for composition come from all kinds of backgrounds but need a portfolio of 3-4 pieces and letters or recommendation. Some have been to conservatory, some studied physics in undergrad, or literature and everything in between. Composition is a long journey and an argument can be made that a broader education can contribute to it over the long term. An argument can be made for career building as a conservatory undergrad as well.
Have you read the Double Degree Dilemma essay posted above in this forum? It is really about different ways to study music, using specific hypothetical individuals as examples. Which does he resemble?
He sounds multifaceted so perhaps a BA or double degree program would serve him best. Lawrence, St.Olaf, Oberlin, Bard, Ithaca, Hartt all offer a double degree as well as a BM. Bard actually requires a double degree of conservatory students.
If he does not want to do a BM then he might want to check and see if the conservatory BM students get the best teachers and performance opportunities, and if that is the case, avoid those schools despite the presence of a conservatory on campus.