There's no official time frame, so you'll get different answers. Also, generations are somewhat arbitrary delineations that are defined by things other than age, particularly major events and themes that occurred in early life.
For example, it seems that "millennial" is congealing around 1981-1996, at least according to Wikipedia, but there's still variance. https://en.wikipedia.org/wiki/Millenial#Date_and_age_range_definitions
Retro: SNES and GBA. I have strong 16-bit nostalgia, but I also think the pixel graphic art style of that era has aged much better than the low polygon count, early 3D art style of the N64, Saturn, and PS1. Some modern, usually indie games get pixel art on the same level, like Sea of Stars and Cobalt Core, which I have enjoyed.
Current Generation: Steam Deck. I barely play anything else anymore and I'm seriously considering only keeping a Steam Deck or similar portable for the next generation. The other consoles (Switch, Xbox, PS) are all too locked down and are clearly just trying to keep me locked in their ecosystem.