'GRANDPA PUNK'

Ever since i was told to "fuck off and listen to your (me) grandpa punk" Ive been trying to work out just how a band becomes a grandad band, is it bands from the 1960's garage punk scene? or the MC5/stooges/dolls era? or maybe every band between 1976 and 1985?.
i know, its bands that formed after or around the change in century, say, every band like your blinks and your sums, but if so, what about bands that formed in the 1990's and are going strong at the moment?, no no, its bands that are not 'nu-punk' and who play 'older styles' that are 'grandpa's'.
on refection i think that there is no such thing, why cant a 'punk fan' listen to bands from any era they like? i know i do, it gets dull if you stick with one type of era or sound and i think the 'grandpa's' are the ones who wont give anyone not in their idea of 'now' a chance, their 'stick in the mud' attitude is not very punk and makes those 'grandpa's' miss out on a lot of good bloody records, their loss.
mixing say, the stooges with zero tolerance and 17 stitches etc etc, is healthy i think, better than sticking to a tiny portion of punks musical legacy and becoming an ignoramus about the music you claim to like.
there i think Ive sorted it out in my mind to my satisfaction.