???
.
you gotta quit driving backwards ........

seriously, a few thoughts ........ guesses .......
.
the front calipers may need some help .......
.
a 'proportioning' valve (or whatever) could require adjustment replacement .....
.
brake fluid level - flush ........ ???
.
it could be parking brake related - if the parking brake actuates the rear pads. If the parking brake system is comprised of small shoes that operate inside a small drum on the rotor, the parking brake action, adjustment, etc is probably not the issue.
.
Although it is not common for rear pads to wear before the fronts - it is not *totally* uncommon. Some mid-90's Accords were known to wear rear pads as fast as the fronts - and sometimes before.
.