Your presupposition is flawed. Not all bodybuilders from the 60's on did steroids. Vince Taylor is one of the oldest competing bodybuilders and he has never touched a steroid. He is very conscientous of his health.
You might also look into the "Colorado Experiment" if you believe that steroids are a prerequisite to muscle gains.
Most doctors will tell you that steroids are not a requirement to build such a physique. It is very much genetics, combined with diet and exercise. All steroids do is increase protein synthesis.
A lot of lazy and ignorant people throw steroids out as an excuse for their own shortcomings. "Well if I did steroids..."
My answer to that is "Well if you got off your couch..."
Here's what Dave has to say on the subject: