Cows - a couple have reached around 20.
We have a significant number of 12 - 16 year olds that are quite happily spitting out the calves still. Have two that have no teeth yet still get along alright without any extra feeding.
Bulls - have two mature bulls now, one is 12 (had him since 2y.o) the other about 7 (had him since 3 y.o). 12 year old has lost some teeth and has a bit of arthritis in the back legs, but still gets his job done. He produces amazing calves, we will not be letting him go any time soon (he will be here till he keels over, I think)