For those who have not seen Grandpa Rex's Allen, CNN has a story on their website along with a short video clip of him at his 33rd [sic] birthday in February 1998.

Cats and Kittens Magazine made Grandpa their Cat of the Year in 1999. They note he died on April 1, 1998 at the age of 34 years, 2 months, and 4 hours.

I do not know how old the oldest cat is.