I have a 28yo Quarter Horse and his only real problems are a bit of arthritis (which isn't bad, we haven't had to do anything for it yet. He just gets stiff), his vision isn't great anymore, but he still sees fine on his own and he's losing some teeth so we have him on senior feed. We did the beet pulp thing a couple of winters ago too when he first started losing weight. He's doing fine now though :)
I have 24 yr old Appy gelding. Not really too many issues. He is harder to keep weight on, and he is more prone to choke with pelleted feeds and has a week tendon (old barrel racing injury) but other than that he's not much trouble. The weight issue is solved by making sure he gets to eat where he doesn't have to compete (in a stall for his pellets, which are soaked and that stops the choke issue). He still eats hay just fine and he's still very active. I'm sure there is some arthritis there somewhere, but he doesn't show it, yet. The old bow in his tendon is something to keep an eye on, but that's not age related, just an old battle scar, as I call it.
I think the most inconvenient part is he has a sway back so fitting a saddle takes more effort than on a younger, healthier horse.
My old man is a 29 yr old Appy named Cheno. He's been here for 17 yrs. He suffers from ERU and went blind a few years ago. Basically the blindness, some missing teeth, and achy joints are his only issues. So he gets beet pulp, alfalfa pellets, Total Equine and MSM along with grass and hay.
Well my horse is not yet old. BUT your old-timers sound so fit and healthy. So I really hope that when my horse becomes that age...he'll still be sound and healhty and full of life like your guys
I have a 32 year old POA. He has some mild arthritis, has lost his molars and premolars and he's got a sarcoid on his p*nis. But he's fat and sassy--comes running when I call him to eat and plays with my young geldings in the pasture.