This!!Rouge H is an amazing color. However, note that it looks radically different on different leathers.
1) Yes, it's a neutral, in the sense that navy is a neutral IMO. Since "oxblood" became so popular it's as though trends caught up to Rouge H.
2) I think year-round depends more on leather, not colour, so I will say yes. It's more about appropriate setting: you would not take a Rouge H box Kelly to the beach (well, I would not) but you can certainly take to dinner in Manhattan any night of the year.
If you are thinking about a Birkin, you will probably be looking at Togo, Clemence, Epsom, or maybe Box or Chevre if you get lucky. Rouge H is beautiful in all these colours but currently in Epsom it's very brown. It's still a lovely colour (if you like Epsom) but not the deep red we usually associated with RH. In Box it is stunning.
I am totally perplexed by how a colour can be an age but thats just me
Rouge H to me is a neutral - it looks fabulous with almost any color and can be worn with practically anything. I also think it is dependent on the leather as it can looks very brown in some leathers but the Rouge H that I love is the wine/cherry color that you usually find in vintage box calf.
I also think it can be worn year round though less often in the summer. I think Rouge H is more versatile than black (which I only wear in the winter) and looks good with anything from jeans to flowy sundresses but again, it depends on the shade and leather.
Also, I never associate color with age -- anyone can wear any color at any age. It's the attitude, not the color, that makes the difference.