Cats listed on this page for adoption are aged from 8 years. Considering that cats can live, if properly cared for, anywhere up to 21 years of age, then 8 is hardly a drop in the bucket. The average age is around 18 years.
The permanent residents of the shelter are around 11 years old at the present time, ie Lexie, Tarsha and Scooter and honestly they behave more like 2 year olds. The biggest advantage of an older cat is that it already knows all the ropes and if it's being adopted later in life I generally find that the cats really appreciate a secure and loving home when they find it.