Josh Brolin -- Good Genes or Good Docs?

Josh Brolin's good looks are out of this world!

Here's a 15-year-old version of the 'Goonies' star back in 1983 (left) and 35 years later ... the now 50-year-old father of two was photographed at the "Avengers: Infinity War" premiere earlier this week (right).

Marvel-ous.

The question is ...