Floyd Mayweather -- Good Genes or Good Docs?

Floyd Mayweather's good looks are also undefeated!

Here's a 21-year-old version of the fresh-faced professional boxer after winning a fight back in 1998 (left) and 20 years later ... the champ -- who celebrated his 41st birthday earlier this week -- at the All-Star Game in Los Angeles (right).

Knockout.

The question is ...