Prior to 1980 they could have served one week of active service and been eligible. The law changed in 1980 so that they would have to have served for 24 months. That is your regular service person. I'll use me as an example. I served in the seventies. I served a two-year enlistment, and I'm eligible. If I had served 20 months instead of 24, and I had served in 1985, I would not be eligible.
On March 9th, 2009. See this statement in context.