To answer the question about what makes a bike “retro2….
On retrobike.co.uk the cutoff is 1997. Reason for this is summed up by a moderators post on RB about the very same question:
The 1997 date makes sense to me due to a number of technical changes and advances as seen on the widespread introduction of a number of components.
These included, the introduction of V-brakes, forks like the Marzocchi Bomber which were reliable and performed well and disc brakes became much more affordable and popular. There was also the introduction of Shimano’s 4 arm chainsets.
Full suspension was also becoming accepted as not just for DH. Bikes like the Santa Cruz Heckler, GT LTS and the Marin Mount Vision proved to work well for general trail riding and XC racing too.
In 1997 in the UK, the first purpose built trail centres, notably Coed-Y-Brenin had just opened. This was a very significant step which has fundamentally changed and shaped mountain biking (at least in the UK) ever since.
Mountain bikes and mountain biking took a significant evolutionary step forward at around about this point so it seems to be about the right date for me.
But as already stated, it has already been a thoroughly discussed subject in the past.
EDIT: The more I’ve thought about it, the more significant the opening of the Red Bull trail was back in 1997. I visited it for the first time in November 97 and came away thinking that this was a great new experience to have on a mountain bike. Marked purpose built trails where bikes had priority. It was like racing but without the entry fee or the need to compete.
Everything was different after that.