Look at his Adjusted OPS+ numbers at b-r.com. Bonds' best OPS+ prior to his 2001-2004 run was back in 1993 -- 206. The only other time his OPS+ was over 200 was the previous season, 1992, when it was 204. He was 27-28 years old those seasons.
Fast forward to 2001, when he begins the season aged 36 (turns 37 in the summer), and he puts up an OPS+ of 259. Next season, it's 268. Then in 2003 it's 231, and in 2004 -- the season he turns 40 -- it's 263.
So he's shattered his personal bests roughly a decade past his "prime" -- and by prime I mean his natural, biological, God-given, un-juiced prime. He's not only shattered his own records in those 4 seasons, but 3 of those seasons represent the best ever OPS+ years ever.
To put this in perspective, let's look at the players Bonds was compared to in the initial post above. Here are their best OPS+ seasons, and their ages at the time:
Ruth 255 (25)
Williams 235 (22)
Mantle 210 (24)
We'll never know what sort of numbers Bonds would have put up those 4 seasons without juicing, but I think it's safe to say he wouldn't have improved so much on his previous bests. In fact, I think it's reasonable to assume that he wouldn't have matched those previous bests.