I used to buy pre-crushed grain a couple hundred pounds at a time and use it over a period of months. I never really noticed a difference vs grinding on brew day.
I think the perishability of ground grain...and grain in general...is overrated. Keep it dry and cool...all the stuff that is intuitive...and you're fine as far as I can tell. I've used some very old grain before, and never noticed any problems. YMMV.
Oh don't give me none more of that Old Janx Spirit
No, don't you give me none more of that Old Janx Spirit
For my head will fly, my tongue will lie, my eyes will fry and I may die
Won't you pour me one more of that sinful Old Janx Spirit