I think that the past is always a construct made by our (collective) minds, and as such any notion of an era or "generation" is just a fabrication. I was born in 1976 and I was a teen in the early 90's, and that's what I feel is "my era", but when I was living it, it was just "life". Now 25 years later, I think this is the shortest time frame that the cultural hivemind needs to start building a coherent picture of the "90's" as an era with it's own aesthetics and music etc. The 00's are still "in the making" I would say.
The Wikipedia article about "Hauntology" had these nice lines:"
In the 2000s, the term was taken up by critics in reference to paradoxes found in late modernity, particularly contemporary culture's persistent recycling of retro aesthetics and incapacity to escape old social forms.[3] Critics such as Mark Fisher and Simon Reynolds used the term to describe art preoccupied with this temporal disjunction and defined by a "nostalgia for lost futures."[2]" So that made me think that the need to have retro-sentiments is some basic (post-modern Western) human need maybe? Overall I don't feel that Vaporwave's fetishization of the 80's is about a particular generation's nostalgia, but it's an emotional cultural structure filling some need of ours to feel certain kinds of feelings about the "Now" by filtering our experience through a mental construct projected into an imagined past.
SO to answer your original question, I don't believe it makes any difference when you were born, in regards to being "entitled" to feel certain way about Vaporwave, or anything else in this world for that matter.
I've always felt the same way about the (late) 60's; for me and my teenage friends that was the era we idolized and felt bad that we weren't alive then. Well, I gotta run now but this is a very interesting subject..!