The classic Vaporwave tag may be on the decline because there are many offshoots, and also the sound and aesthetics are absorbed in other genres.

I would say Chillwave peaked around 2009. I was at uni when I was listening to it and I feel to old to "get into" it now.

You are never too old to get back into music you enjoyed when you were younger, if it was any good to begin with.

The only stuff I've found I can't go back to in the long run is the dreck-- the low quality, overly derivative or ethically questionable non-art. Everything else can fly again after you get over being burnt out on it. [That is, unless you grew up in the age of radio dominance, in which case there are probably several good songs that've been killed for you forever through overplaying.]