My poor horse

I think horses that are well taken care of throughout their life are the ones that live on into a great old age.
Ponies, donkeys and mules seem to have the longest life spans. and I agree with Cat about different breeds having greater longevity on average.

A lot of performance horses are started at a young age before they having matured structurally, and are naturally under much more stress, physical stress as well as environmental/ emotional.

I just bought an 18 year old gelding, a former roping horse. He's healthy and sound and very forward and eager to be used. I expect him to be a great riding horse well into his twenties and hopefully beyond. I also hope to be able to keep up with him for all those years.

back when i was looking at going to a college for animal sciences my parents & i went to UVM & checked out their Morgan Horse program. they said that on average for them getting a horse to reach 30 was common for that breed

So how long is a horse useful? I just know them as hay burners.

that's like asking how long are you useful! it all depends on how willing the horse is to do what it/you want to.

Useful is sort of a foggy area. Different definitions to different people. But as far as earning their keep, there is a local horse farm that has a lesson program for beginners and intermediate riders and most of their horses are seniors in the higher 20's.

My white gelding Joe is kid safe. He is priceless to me. If all he does is walk around with grandkids on his back, that is fine with me. Useful? You bet he is.

Cat, I thought I had responded to your post earlier, just wanted to let you know I am also sorry for your loss.
It always amazes me that horses live as long as they do. Their leg bones look so delicate to hold up so much weight and be subject to so much stress.

So sorry Cat! DD lost her horse this spring. She moved her to a new place and some freak accident that nobody saw, but she was on the other side of a fence dead. It almost looked like she flipped over it. Very sad. Horses are special and bad enough for us, but to watch the other horse miss her would be hard. They think that DD's horse bonded with this young filly and she was in the pasture and DD's horse wanted to get in with her and some how tried to get over the fence.

As long as a properly trained horse remains sound he/she is useful. Many horse sports are very hard on their bodies. Internationally, several horses have dropped dead because their hearts stopped, yet horses have no known heart disease.
People buy horses with their eyes and their hearts and often turn their brains off. So, you get horse owners that care for chronically lame/chronically sick horses that were that way when they purchased them. Just like dogs and cats, there are waaaayyyyy too many unwanted (often lame and/or sick, but usually badly trained or unmanageable) horses for people to own them. The term "pasture pet" should only apply to a horse that has worked hard, lived a long life and cannot work but has earned his retirement. That was my 13.2hh big barrelled pony, Toma who taught many children and timid adults how to ride, but his 10 or so years on the trail rig before I bought him caught up to his front legs, later in his 35yo life. When we trailered out and left him at home he would cry and probably would have raced down the road after us, if he could. He still WANTED to work. When we stressed our trailer by loading up 5 into a 4 horse stock, Toma would load himself in the middle of the back of it between the other 2 horses already loaded.
Training, attitude and physical fitness for work determines how long a horse is useful.
I could write a dissertation on this subject...so I'll stop here.
BTW, we paid for that down the road when the back axle was bending. But, we were blessed when the guy in the middle of South Dakota that couldn't fix it shaved off the metal that the tires were rubbing on and the semi-truck shop in Rapid City, SD bent it straight and added heavy duty shocks to it, which were far better than it had ever had before. Our mechanic put in a new axle after our vacation.

That's what it's all about.