whole grain stays fresh for quite a while when stored correctly and if by "fresh" you mean stored in a grain bin for month(s), bagged and shipped to a distributor, then stored a little bit longer, then bought by your LHBS shipped again and stored there until you can along and bought it and took it home ...you mean that freshness?
If you grind your grains and try to store them they will go stale rather quickly I have held onto crushed grains for 4-5 days before using them and I would suggest going no more than a week or so w/o using them before they start noticeably losing their freshness IMO.
You can still brew and make beer with them, you just will not get the same flavors out of the same grain if it were freshly crushed ...it will be diminished to a degree.
if your grain does seem stale to you just add more hops! ...a stale pale ale?