Quoted By:
Depending on when RSE is set, and Steven's actual age, he could not be born in the 1970's at all.
If you think it's set in 1995, and see Steven as a 55-year-old and his dad being 80, then they would be born in 1940 and 1915. (his age is ambiguous, his hair looks blue but it might be greying.)
But i'd say his dad might actually be 45-50 (at least), making Steven around 20-25. Which yes, if you consider RSE\RBGY to be set around the time they were released, he is born in the 1970's. But i do not think they actually said the year in any of the games. For all we know he's a 34-years-old from year 2025.
(Correct me, did they actually say what year it was in some of the games? But it has to be at least after the sixties as you can see in Surge's gym they actually say there's a shuttle from 1960 or something.)