Sadly both of our old gals passed away this year (R.I.P beautiful girls!) but they both worked right up through their late years.
One mare was named Pudding. She was just an old sorrel mare with no papers or anything, but we loved her to death. She was ridden from age three up into her twenty ninth year, when her artheritis started getting too severe and she began dropping weight rapidly. We had her euthenized last week and will sorely miss her.
The other mare was our miracle horse, Delriah. Old Del lived to be an astounding fifty years old and she was ridden and 100% sound up into her 49th year. Actually, she refused to be retired. We aquired her in her thirties, and had been told that she was an early twenty year old. When we found her real age and attempted to retire her from being an advanced lesson horse though, she became very depressed and lethargic. As soon as we put her back in, she was right back to her old pushy, high energy self- bossing everyone around. She finally told us last winter that she was finished, and was retired for two months before she laid down and died peacefully.
Horses know when they can't continue, and they'll let you know if you listen. Many of us try to limit our animals by their age, but that only does harm. We loved our old gals with our whole hearts, and they enjoyed their work. Why should we take something that they enjoy away from them?
Pudding at age 28
Delriah at age 50