Jeff Bridges -- Good Genes or Good Docs?

Jeff Bridges' good looks have some serious grit!

Here's a smooth shaven 27-year-old version of the "King Kong" actor back in 1977 (left) and 40 years later ... a much fuzzier version of his dudeness -- who turns 68 this week -- at a Los Angeles event last month (right).

"Strikes and gutters, ups and downs."

The question is ...