Complex sentence: He relocated to the United States when he was 10 and obtained his Ph.D. in Philosophy from Princeton University in 1951, the youngest person--22 at the time--ever to do so in that department.
Split into simpler sentences: He relocated to the United States when he was 10. Thereafter, he attended Princeton University, graduating with his Ph.D. in Philosophy in 1951 at the age of 22, the youngest person ever to have obtained a Ph.D. in that department.