Complex sentence: Hissey has an association with St Mary's Cathedral which has spanned the past 45 years being accepted as a choral scholar to the "St Mary's Cathedral Choir" at the age of nine and completing his schooling at the "Cathedral Choir School".
Split into simpler sentences: Hissey has an association with St Mary's Cathedral which has spanned the past 45 years. He was accepted as a choral scholar to the "St Mary's Cathedral Choir" at the age of nine, completing his schooling at the "Cathedral Choir School".