If you want to age a new leather jacket, there's no substitute for simply wearing it as often as you can. Sometimes, however, you don't want to wait for that rough-and-tumble lived-in look. Frankly, you're in very good company if you feel that way. Hollywood costume designer Deborah Nadoolman had to artificially age ten new leather jackets for the first Indiana Jones movie in a very short period of time. You can apply some of the same techniques to make your new leather jacket look old.
Spray a little rubbing alcohol on the surface of the jacket, using a spray bottle, or lightly apply rubbing alcohol, using a toothbrush. The jacket should be damp but not drenched: the alcohol will dry it out in points and help create a weathered look.
Rub sandpaper on the leather to give it a worn look. Sandpaper with a fine grade works best. Focus on portions of the jacket apt to see a lot of wear, such as the elbows, the shoulders and the pockets. You can apply the sandpaper to other locations in order to represent casual damage but take care not to overdo it. Some parts should look worn and others shouldn't be touched at all.
Apply a wire brush to the jacket in the same manner you applied the sandpaper. Center on natural wear spots like the elbows and pockets, with variations here and there to give it a naturally aged look.
Go to a sandpit in a nearby playground, wad the jacket up into a ball, and kick it around in the sand. Pick it up, dust off the excessive dirt, and then repeat the process one or two more times.
If you have access to a long driveway or a private length of dirt road, tie two lengths of twine to the bumper of your car and duct tape the other ends to your jacket. Pull the jacket up and down the roadway with your car, checking often to ensure that it's not becoming too aged. This method also works with a bicycle on a dirt trail. Make sure the leather side is facing the road, not the interior shell.
When making a new leather jacket look old, slow and careful are the watchwords. You want to give it the proper aged look without damaging it or ruining it. Accordingly, take your ageing process step by step, and check whenever you are done. Small increments will allow you to determine when it's aged enough, but bigger steps could make it more distressed than you wish. Remember, once the jacket's aged, there's no way to "un-age" it.