The old man finally passed away at the age of ninety.
Tips
culture
归西 is a Buddhist-influenced euphemism for death. The 'West' refers to Sukhavati, the Western Pure Land (西方极乐世界) of Amitabha Buddha, where souls go after death. It carries a gentle, accepting connotation.
register
归西 is a polite, somewhat literary euphemism. It avoids direct mention of death (死). Similar in register to English 'pass away' or 'go to a better place'.