Here is my 2cents
My son plays about 120 -140 games a year and gets about 2 years max out of a glove before it seems like its time to replace. He is an OF. On the other hand as a fun note I had a Rawlings 12 inch from my teen years that was about 25 years old. I sent it out to be reconditioned (ie new palm padding leather conditioning, re-lace) and gave it to my lefty 10 year old daughter to use for softball and it works great and she absolutely loves it and cherishes it since it was mine.
I would say as a general rule of thumb
IF 1 year or a little more.
OF 2 years or a little more
and it all depends on the quality of the glove and leather used, and how well you care for it. Don't let your IF put it in his bag and smash it up. You will see most upper level guys hang theirs on the outside of their bag (using a carabineer or whatever) to ensure they maintain a good shape.