Original: At the age of ten, Walton was accepted as a chorister at Christ Church Cathedral in Oxford, and he subsequently entered Christ Church of the University of Oxford as an undergraduate at the unusually early age of sixteenKennedy, p. 6/7.
Simplified: At the age of ten he joined the choir of Christ Church Cathedral in Oxford. He was only 16 years when he went to University of Oxford where he was at Christ Church, Oxford.