You'll find in general parlance around here, people will talk of "Umbrae-ing" a deck. This term was coined after Umbrae described a method of softening stiffening cards - but it will contribute to the look of them as well. Then there's ultra-fine sandpaper to rough-up the laminate, followed by swabbing with black tea, which I'm sure we all know.
Also, *use* will do it, better and more authentically, because all the cards will be different.
You'll also find around the boards, a great deal of discussion of people who have noticed a flaw, a tiny stain or scratch or bend, on their deck, whbich they think makes the deck unuseable for them! <laughter> I see more discussions based on preserving decks or replacing individual cards that might be starting to show signs of aging, than I do on deliberately aging cards ahead of time.
Bear in mind, that most if not all methods of aging them, will also con tribute to them wearing out sooner than usual. If you particularly love a deck, and it goes out of print (which they do, regularly!), and you have artificially aged it, and then with wear over teh decades it becomes unusable, you might live to rue it bitterly.