How to age playing cards? There are already very nice answers about paper on this and the rpg section, but playing cards are a little bit different and at the same time more specific as they have a special finish and a certain type of paper used.

There are numerous recommendations about roughing up the surface and then using tea bags (for an aged brown look and to oxidate the ink, this sometimes has the sideffect of a teasmell though which of course should be avoided for realism), scratching up the surface and using oil (simulating the play history, as in handoil and nailscratches) and applying coffee to the edges (as they are more exposed there is more wear on these parts),

but how do you get the best results now if you want to make your playing cards seem as if they have been regularly used for a long long time (but this, in a preferably quite short time)?
Work the cards. That would be the only way to make them seem used for a long time. 

What you would want to do is learn a few ways of shuffling (ie. overhand, riffling and cascading. There are tons of examples on the web.) No need to use any fancy techniques, just basic card handling. Then just constantly work the cards until they are broken in. 

It may take some time (maybe a day or two) but you can shuffle as you do other things. You just need to flex and rub the cards together for a length of time, concentrating the working of the cards over their lifetime into a few hours. That combined with the visual aging methods you describe will give the cards a used look and feel.