I'm pretty sure my grandfather was probably in his early sixties when he died. ... Since he died 23 years before my grandmother I'm thinking he was about 62 at the time.
Forgive my nerdy detailing here (but I love to reconstruct this type of stuff); if your grandfather was about 62 when he died in 1977 that means he was born about 1915. Your mom was born in 1935, so that means he was 20 when your mom was born. If he married at an early age thats certainly reasonable.
