Complex sentence: He was an indifferent student with a liking for mathematics, flying, and things mechanical, taking his first flying lesson at 14, and later attended math and aeronautical engineering courses at Caltech.
Split into simpler sentences: He was an indifferent student, with a liking for mathematics, flying, and mechanics. He took his first flying lesson at 14, and later attended math and aeronautical engineering courses at Caltech.