I don't think it's fair to ban all pre-1992 cars from entering a city, but 1992 was 15 years ago, ordinary cars depreciate to a cheap price well before that length of time, they won't get much cheaper once they've depreciated to certain price. So if you can't afford to buy something like a 1993 Ford Fiesta you can't really afford a car anyway.

However when they say pre-1992, are they just trying to get rid of worn-out old bangers? What about someone with an 80s Porsche in good condition? I think in Britain they once tried to do this kind of thing to get rid of really old bangers (a car that is completely worn out and falling apart).