Jay Z: Good Genes or Good Docs?

Jay Z’s got 99 problems, but aging ain’t one.

Here’s a 27-year-old version of the New York rapper mean muggin' a camera back in 1996 (left) and 19 years later ... the Rap boss and father of one -- who celebrated his 46th birthday earlier this week -- at a Madison Square Garden event earlier this year (right).

Hova!

The question is ...