For how long should an individual’s training record be kept after they separate from the Army?

2 years is the time it should be kept, unfortunately, its usually trashed a few months after.

If you are working for the DOD once you get out of the military, you should be able to track your training records. For example I was in the US Army, when I retired and started working for the US Army as GS civilian, I was able to get all of my records from AKO and ATRRS and ALMS. You may want to check if you can do the same from other platforms from the other services.

The appropriate time is listed in the designated ORL in ARIMS. Which specific ORL the unit has assigned to Training Records varies from unit to unit.