I've recently been weathering my ghostbusters boots, and I found the best thing to do was just to wear them to work for a couple of weeks.
Although this is probably not an option for you, so x2 on the mangling and maybe a few cycles of wetting it, drying it , beeswax. And maybe let it sit somewhere dusty, if it's a jawa costume maybe drag it though some sand repeatedly Depends how aged you want?