There are a couple of possibilities. If you use inserts, your ring finger insert might be slightly too tight. That'd probably be my last guess. More likely, you're hitting harder on release with the ring finger in order to create more revs. When I want more turn on the ball, I put more pressure on my ring finger. When I want to stay more behind the ball, the pressure is on my middle finger. If you're constantly applying added pressure to the ring finger to get more lift and turn, then it's going get more wear and tear than your ring finger.
That being said, the pads of the fingers shouldn't be callused. That indicates that you're hanging onto the ball too long during your release in an effort to "grip and rip" it. If you have calluses at all, they should be just above the first finger joint.
I mostly see calluses on finger pads from the kids I coach who are trying to no-thumb the ball. I'd suggest going back to your pro shop and showing him/her the calluses. Ask about adjusting the pitches. And then find a qualified coach who can work with you on getting a cleaner release that will eliminate the undue pressure on your finger pads.
Deb