John Travolta: Good Genes or Good Docs?

John Travolta is stayin' alive.

Here's the 23-year-old "Saturday Night Fever" disco dude back in 1977 (left) -- and 35 years later, the 58-year-old "Battlefield Earth" hunk in Paris on Friday (right).

Face/off.

• Obama vs. Romney
• Kyra Sedgwick
• Jennifer Grey