Two primary ways to decide what is considered 'oldies' by society.
1. If you hear it in an elevator, it might be an oldie.
2. If Sirius/XM has changed the decade channel location/name, then it is definitely an oldie.
i.e., '60's on 6' is now '60's Gold' and no longer on channel 6.
Same thing happened to '50's on 5' many years ago. It is also now '50's Gold'.