Its better to take pics on drive side. Most components have date codes you can look up. If they are original, that will tell you age. I have found codes on seat post, handlebar stem, handlebars, quick release, hubs, freewheel, crank arms, and both derailleurs. Look for the oldest codes, get ones that are a few months apart, and you probably have the age of the bike (recognize that bike would be built from parts off the shelf, so bike could be six months newer than components),
Vintage trek site has great detail on component codes (not limited to Trek bikes in any way).