Rear brakes wearing faster than front.

If there is not a proportioning valve set up could be a master cylinder, e-brake engaged, Calipars on front may need rebuilt or missing parts or guide pins & bolts are worn, The pads themselves on front may just be crystallized and need replaced, if this is the case then the rotors need turned too or replaced. I would think about using a full rebuild kit on front brake hardware, as-well as the rear brake hardware, adjusters too. If there is not a proportioning valve then the master is doing the proportioning. The front is and should be bearing the main brunt of the braking thus wears out faster. If the rear is wearing the evenly then its likely the master cylinder or a proportioning valve, but if not then the other thoughts above will apply along with new rubber brake lines from steel line to calipars.