Doesn't look like it's in his prime. Aaron's best years were when the Braves were in Milwaukee, and that photo was taken after they had moved to Atlanta (evidenced by the "a" on his cap). I haven't read it yet, but Aaron has an autobiography called "I had a Hammer" that is supposed to be superb.
Incorrect.
When Aaron played for the Milwaukee Braves he averaged 33 home runs per season; after the team moved to Atlanta he averaged 37 home runs per season.