"There are those with 20 year service collecting retired pay who don’t qualify for VA benefits." VA medical benefits. All the rest of them, you get so long as you've served 180 days of continuous active duty time. The VA medical benefits can be much more tricky to acquire, primarily due to supply and demand.
The caveat I should have added is that the 180 days must be served while on a
federal activation, like the one Bush signed shortly after 9/11. State activations (and of course, I'm speaking about Guardsman), don't count towards VA Benefit eligibility. As such, since 1980, many Reservist and especially Guardsman are foreclosed from benefits if they didn't serve 24-months of active duty time. That was a relaxed a little with legislation passed a few years ago, and
I think that 24-month requisite only applies to medical benefits.
Even still, the VA is so overburdened, people who serve years on active duty have difficulty securing care via the VA unless their condition is directly related to service injuries. It's a criminally uncovered problem with the VA.