And he's the youngest man ever to reach that plateau, beating Jimmie Foxx by 79 days. Foxx finished his career significantly below the career home run mark, at 534 (that's 180 behind Ruth). This seems to be because his career went downhill earlier than one might expect given his historic level of ability. At 32, in 1940, he lost 50 points of OBP from the previous season, though that wasn't his career low, that having been set in 1937 (I'm only considering his full seasons).

He also lost about 80 points of slugging and hit only half as many homers as he had the year before. The season after that he was traded mid-season and had the worst half-season (he only played in 100 games) of his career, hitting 226/320/344, though that OPS put him not far below league average, as it was good for a 93 OPS+. He missed 1943 and almost all of 1944 (he had 22 PA's in '44), probably because of the war, though he was 35 in '43, so I guess he wasn't drafted.

He came back in '45 and hit respectably, posting a 112 OPS+ in 248 PA's, though that's far below his established norm. He retired after that season.

So after 1940, before America was drawn into the war, Jimmie Foxx had hit exactly 500 home runs. Despite being just 32, he managed to hit only 34 more in his career. That's half a Barry Bonds season spread over four years, and this isn't Rey Ordonez we're talking about. Bonds at the age of 32 had well less than 500 homers but here, five years later, he's at 613 (or rather, 614 after his one so far this season).

The moral is that while Alex Rodriguez certainly has a lot of things going his way to make a run at this record (great ballpark to hit in for the next seven years or so, a good lineup that's going to get him more plate appearances by scoring more, a record of good health), you never know what can happen in this game.