well i'm kind of new to this, but one thing i know may be of use to some of you.
here's my personal method for makin leathers looked older and more worn with out all the years of use needed to get them there.
heres what you will need
1. prestained leather
2. turtle wax rubbing compound
3. terry cloth
4. kiwi shoe polish
5. rough colth for applying shoe polish
6. soft cloth for polishing the shoe polish off
photos arent as good as i like because i had to use my cell phone to take them sorry
ok first you take the leather that you stained already and apply the rubbing compound in circular motion until uyou have the entire surface covered, next use your terry cloth to rub the compound off, the harder you press and the more times you repeat this step the lighter you'll make the stain.

this is an untreated piece

and this is after the rubbing compound
now that you've finished with the rubbing compound it's time to use the shoe polish same as before apply the polish in a circular motion covering as much of the surface area as youd like to darken back up again, once its on you the polish it off with a soft cloth if you let the polish set on too long and dry it becomes a harder to remove, but this does have the added effect of appearing like smudges and extermely dirty areas.

and this is the finished product as i said the pics are kinda crappy and i apologize, in this example i have presented i have used a tandy eco-flow stain called dark chocolate it's an almost black brown, that when the treatment is applied becomes mush lighter and all of the divets and cuts in the leather remain black having a very nice aged effect when your done.
this has worked very well with many different stainn colors i've used so far, so good luck and i hope this has been of help to some of you