'McSteamy' Eric Dane -- Grays Anatomy

Move over Anderson Cooper -- "Grey's Anatomy" star Eric Dane (aka McSteamy) upped his silver fox game to a new level this week in Mexico -- rocking the hair of a man twice his age ... and the body of a man half his age.

41-year-old Dane and his 42-year-old wife Rebecca Gayheart were photographed as a twosome Tuesday -- looking hot in their pool gear -- and Dane's hair is whiter than ever.

It's true ... age really is just a number.