What should be the maximum height for a 12.2hh 10 year old pony to be jumping?

Whatever the animal is comfortable with. He'll let you know when you've reached his limit :)
As high as the pony is comfortable with.
I would do about 2 ft 3 in. That is the hight that a pony that size would jump in a rated show. At the max I would jump 2'6
I would ask my vet because that depends on a huge number of things, breed, physical condition, rider size, conformation, etc. There's no one answer for all ponies that size and age.
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