Difficult to put a number on it! I think this is based on lots of personal factors such as weekly consumption, affordability, age, storage space and no doubt others.
My loosely-defined aim is to have a conveyor belt of ‘nicer’ wines in the £15-25 bracket (maybe more for birthdays and Christmas) which I can enjoy once or twice a month. I’ll supplement these with everyday drinkers bought at the time from TWS or the supermarket. I definitely prefer the more savoury, complex aspects of mature wine but wouldn’t want to (or couldn’t afford to) only drink older wines.
I probably have about 80-90 in that nicer category in various nooks and crannies at home plus in reserves, so plenty to keep me going - although most still need at least 3-4 years before I’ll open them so I haven’t really started enjoying the benefits of that conveyor belt yet.