Although we draw no inferences regarding the steroid controversy from our comparison of their careers, it does appear that the career patterns of Henry Aaron and Barry Bonds are really not as dissimilar as many claim. As critics frequently have noted, Bonds did indeed increase his HR output later in his career, but the first half of his career was played during a period that was tougher for hitters than beginning stages of Aaron's.Aaron, of course, did not live in the steroid era, unless you count cortisone injections. Also, as I recall, 1971 was a particularly tough year for hitters, so the comparison of 1971 and 2001 may be more flawed than it seems. Still, the fact that Aaron and Bonds had similar career trajectories, regardless of the differences between their respective years as major leaguers, is an important one to remember in light of all the insinuations made about Barry's power surge in his mid-thirties.
Nevertheless, Aaron's best single-season homer output (47 in 1971) occurred at age 37, which corresponds to Bonds hitting 73 in 2001 at age 36. In fact, there is little difference between Aaron's simulated seasons and the corresponding actual seasons for Bonds -- except for that magical 2001 season. It also should be noted that Bonds, even with the loss of most of the 2005 season to injury, has managed to sustain his HR output a little longer than Aaron did.