Definitely he could have been. His teammate Tom House said that steroids were rampant in the early 70's and two of his teammates went on to manage teams with notorious steroid users (Davey Johnson and Dusty Baker). Aaron had some of his best years from 35-40. All circumstantial, but enough smoke to say that it is impossible.
Sure, late in his career. But there's no evidence anyone in baseball was using steroids before 1970, and by that point Aaron already had 550+ homers in the books. Greenies are a different story, of course.
