The file that you uploaded originates from here: http://www.tsl.state.tx.us/governors/modern/bush-p06.html. It was taken when he was in the Texas Air National Guard, somewhere between 1968 and 1973. Being born on July 6, 1946 (and depending on whether this picture was taken before or after July 6) that would make him between 21 and 27 years of age. I'm sure that can be narrowed down some more, maybe comparing it to other pictures of that period.. ;-)

This picture was the source of a whole lot of trouble during the last electoral campaign since he's wearing an Air Force Outstanding Unit Award and a Small Arms Expert Marksmanship Ribbon, none of which award was officially listed anywhere. There's a discussion on this much cited forum http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=132x654437 about the date of the picture, and apparently it was taken around 1970, which would make him 24. Also check http://www.command-post.org/2004/2_archives/014794.html for the story.

Who cares how old he was! He still looks like a frigin moron!