Totally agree with the other commenters depends on what their are doing how often they are ridin what they used to do. My 23 year old consistently jumps 1.10-1.20 because she has maintained her fitness and is co tent doing so where my 13 and 9 year olds don’t jump over 1.05 because they don’t have the fitness
Depends on fitness level, ability and training.
It all depends on the horse. Some horses can’t do many things at that age and some can do everything that they could when they were 12!
It depends on the horse, the average i would say is to keep it between 18 inches and 2’6
Depends on the horse and it’s ability, every horse is different, start off small and slowly raise it until it no longer wants to jump/can’t