My highest score is 46,551, Retired Janurary 1678, with 76 ships captured.
The next one is 30,652, retired June 1687, with 103 ships captured.
I'm not sure how I managed to get such a good score with the first one - it was one of my earlier games. The 30k game had me capture two treasure galleons in that career, as well as more ships overall, and I was sure I was going to beat my previous high score.
@drkpixie: it sounds like you chose to drink from the Fountain of Youth when you made your character. That's how it works - you don't suffer skill loss and can therefore go on indefinitely.