It doesn't really matter about age, I look for experience and patience, and the ability to read a situation well when around green horses!
16 or older is a good age because you are more responsible at that age
It may vary on your age, training experience, the horse(s) that you will be training and the liability at your barn. Start by contacting them and find out if you're able to start training. If you are then I think any age is fine as long as you're comfortable with training!
It depends on the horse and the person how much experience they both have
It dosent really depend on your age, but your experience with horses and how long you've been riding. But I say 13-14 would be a good time to start.
It honestly depends on your experience but I would say training could start at 13
It depends more on you experience than your age
Hmm, good question! I would say it honestly depends more on your level of experience versus how old you are.
For training horses my trainer says around 16 years old. This is because of liability but it depends on what discipline you're doing.