Most people get a far higher level than is required for the raid (for example, level 80 or 85) and then go in and do the raid with a small group of people from their guild or from the /trade channel.
By all means attempt it, but you'll have a tough time convincing people to come along to an old-content raid unless you're a higher level than it, as most people just want to go along to get the raid done within 30 minutes.
Queues for XP locked BGs have been broken since it was implemented, and there are numerous reported cases of there being sufficient numbers in the queue, but the games never popping. The only reason it seems to work for the lower brackets, is that there are far more players queueing than are needed for just one game to start.
@Alekii most people that lock there xp bar at 60 do it to twink out same as level 70's, and yes you can do at higher levels but its not as fun and the gear is just for show/collection not of actuall use.
and you will actually be suprised about the amount of people willing to help others, its really easy to get a vanilla raid going, like today i went molten core and yesterday went blackwing lair at level 58 with a bunch of higher levels that i didnt know just asked in trade chat,
and you dont need 40 people to do molten core or temple of ahn'qirij, the guild im in has done molten core and blackwing lair with just level 60's and can do all of temple of ahn'qirij except the twins, and they dont use the full raid size, on youtube search the guild im in, theres a couple of vids on there of them doing vanilla raids with smaller groups then raid size supposably needed
I'd like to add there are quite a few guilds like us, all doing retros at level cap. I have seen a couple for TBC content and at least one for WOTLK content.