Cats Real Age?

I was always told that you multiply it by 7, except that when a cat gets over the age of about 15 it starts to get crazy! I haven't met too many cats that lived to be that old though. One of our cats is 70 in cat years (and acts it) and the other is 14, and also acts it. I think it's about right, but as with all things like this it doesn't always work. There's always a limit.