I have some friends at AirBnB and I've heard it's much more modest, like $300/yr or something. My experience with these type of "dogfooding" credits is that companies are much more generous when they're smaller, so it could be that older employees get more than newer employees.
That makes sense. $300 is enough to cover Airbnb housing costs for at least a few days in pretty much any location around the world, so they probably still get value out of it.