Brad Pitt -- Good Genes or Good Docs?!

Brad Pitt's good looks are a real-life 'Curious Case!'

Here's a 24-year-old version of the "Thelma & Louis" star showing off his long locks at a fundraiser event in Beverly Hills, California back in 1988 (left).

31 years later ... the now 55-year-old icon was spotted looking better than ever at the premiere of Quentin Tarantino's 9th film, "Once Upon A Time ... In Hollywood" (right).

The award winning actor stars alongside A-list celebs like Leonardo DiCaprio, Margot Robbie, Kurt Russell, Al Pacino, Luke Perry and heaps of other famous faces.

There's no stunt doubles here.

The question is ...