He's still got two good years to go if he wants to be the oldest living cat ever though, as the current record stands at 29.
Link
Update: He's got at least a good 98 years to go before he catches up to the world's oldest living animal, Jonathan the tortoise. If you click the link, you'll see a great picture of Jonathan from 1900, when he was already around 75.
Link
If one considers Guinness to be the keeper of records on such things, this cat is not currently the world "oldest cat", nor even the current UK "oldest cat" because such a claim hasn't been officially made to them yet. That's where in the article, the Guinness guy encourages the owners to give Guinness a call. If Guinness accepts the claim, it sounds like it would be the current UK senior cat.
As the link notes, Creme Puff made it to 38 and is the world record holder but was a US based feline. Mischief needs to worry about the UK record first...
I've had a couple of 19 year old cats, one of which could have been older. My current geezer will by 18 in the Spring and is doing pretty well. Indoor cats generally live a LOT longer than outdoor-only or indoor/outdoor.