I’m afraid it’s based on the normal TL3 requirements rather than longevity, so you’d have to do a fair bit more reading first. 
Though, as @Jagster pointed out, I am actually making things up and our #lounge is as equally under-utilised as most other commenters on here, so don’t feel like you’re missing out on anything.
This actually sounds a lot like the new setup with the #general category that’s being rolled out for new sites at the moment (as long as you have opened up #lounge to @everyone, that is) - This discussion is general - #2 by JammyDodger I think you’re a couple of steps ahead, but the direction seems very similar to what it will be soon.