How old was Fred Sanford anyway?

How old was Fred Sanford really? Because when Sanford & Son started in 1972, the character of Fred Sanford was 65 years old, which would put him being born in 1907 but later on when Redd Foxx reprised that role on the 1980-81 show Sanford, in one episode where they catch Eddie the thief, Fred said he was Eddie's age(14) in Christmas 1936, which would put him being born in 1922, but in a later episode of Sanford, when Fred was conned by Dr. Matthew Gray, Fred said he was born in 1913 just as the doctor was, which would make him roughly 67-68 years old.