The sign in front of the stall said: Pony, Kiwi: 20 years old; dark brown with black tail and mane.

I would have thought Kiwi was a horse, not a pony. I think Kiwi looks great at 20 years. I have no idea the average life of a horse (Googled it and for horse it can be 25-30 and a little longer for ponies).