I believe you can still get big muscles in your 70’s and 80’s using steroids. But I do not believe an 85 year old man get get as big as he was during his 20’s and 30’s using the same amount of steroids. I believe if you workout and use steroids your entire life—and then stop for a while like the older pro bodybuilders you mentioned did—muscle memory comes into play. But when they get older, no amount of drugs will bring them back to the peak they reached in their youth because our bodies lose type-2 muscle fibers as we age. One day we might figure out a way to stop this from occurring. Either way, we can still look amazing in our old age with what we have available now.