Sadly, Thomas Hardy ale is no longer brewed, but the advice on the bottle was to keep it at least 5 years. Being food, the brewers were eventually forced to publish a "best before" date, but I recall the brewer (or at least, someone senior in the company) being interviewed on radio 4 and he stated that he thought it was best to leave it for at least 10 years.
Which reminds me - I think I have some Waitrose bottle-conditioned Christmas ale in one of the cupboards. I wonder how old that is now?
Edit: the answer is - only a year! 2018 "Vintage" ale. Best before: 2028! Unless I've got a few other bottles lurking somewhere.