How old is grandpa suppose to be (officially) in the texas chainsaw massacre '74?

For the purposes of the movie, I do not think that the real intended age was ever specified or hinted at. But since the movie is based upon the murders carried out by Ed Gein, I would say that since the movie was made in 1974 and Gein was born in 1906, so I would put a possible age of the grandpa character to be at least 68 (but he looked much older - some people do not age well).