Lucy Liu -- Good Genes or Good Docs?

Lucy Liu is getting better with age!

Here's a 31-year-old version of the "Charlie's Angels" star beaming with beauty in New York City back in 1999 (left) and 19 years later ... the multitalented actress -- Who is celebrating her 50th birthday Sunday -- rocking a slick back look at an event earlier this year (right).

Fifty looks nifty on her.

The question is ...