So, how does one take a perfectly new deck of cards and make it look old?
Here are two techniques I employ:

1st. Technique.  For cards that have a gloss or semi-gloss coating, I use a three-step method.

Step One: find a comfortable chair on your patio and sit in it ( a beverage  of your choosing is not a bad accoutrement, either).

Step Two:  Using 000 steel wool (that's what we call it  here in the States). Elsewhere it may be called something different...but it's the stuff some people use to clean their pots and pans. I rub it on the face and back of each card.  This treatment imparts a faded look--as if the cards have been used to the point that the ink is beginning to wear thin.

Step Three: Then I take a pencil with soft graphite--probably #1 lead --and, tilting the pencil until it's almost sideways, I darken a piece of paper with it.  I think you can buy powdered graphite, but I prefer to sit on my patio, beverage in hand, and do it that way (One must bleed for their art!). After I have colored the paper with the pencil, I take each card and rub both sides across the paper.  This furthers the worn look--a slightly greyish hue.  When I am done, I have a nicely aged deck and, depending what I have been drinking, a nicely aged personality.

2nd. Technique.  For cards that are not coated (also can be used on cards that are coated) , I use a bit of soft shoe wax--brown--and rub/polish it into the card.  Depending on the wax you use, you may want to dilute it with the "clear" wax.  Be sure it's soft before applying, or it will streak and not look good.  Then, 40 minutes in a 350-degree oven... (just kidding about the oven.)

Those are my techniques for aging cards. Have fun!

Note. Steel wool is known as Wire Wool in Britain and you must be sure to buy the correct grade (000 is most commonly marked as fine or extra fine grade) which is available from good D.I.Y. and car accessory shops.