When did William Frawly start and end in "My Three Sons",and who was he replaced by ? Also how old was he ?

William Frawley was with My Three Sons from the beginning of the show, which premiered on Sept.29, 1960. He was forced to leave around the beginning of 1965, near the middle of the 5th season, because he was in such bad health that he couldn't pass the studio physical, so couldn't continue working on the show. He was replaced by William Demarest, who played his "brother", Charley. William Frawley died on March 3, 1966, at age 79.