It is perfectly fine to use. The key to grain storage is leaving it whole, cool and dry until you are ready to brew. Once cracked, the surface area is increased and the protective hull is removed more it allows oxidation to happen more rapidy. In addition, the grain becomes highly susceptible to attracting off flavors from anything around it if it is not stored by itself.
'Too long' is really a matter of personal perception for one and what form the grain is in. I am of the school of thought that you can't beat the freshest ingredients possible. Whole grain will last quite some time if kept cool and dry....it has been probably amost a half year now since the last harvest for US barley.
Cracked malt is best kept in a vaccuum sealed bag if you have access to one. A good Ziplock-type freezer bag, with the air removed by squeezing it out just before fully closing it will suffice. Some put the grain into the freezer...if you do, two things to remember: Allow it to come to room temperature before opening to avoid condensation on the grain, and make sure there are no strong odors in the fridge or freezer as your grain will easily pick those flavors up.