It can damage their back and knees
You can start putting the saddle on the horse at around one and a half years. You can start riding it at about two years, two and a half years.
I would do a close contact saddle or for western, a tree less saddle
the saddle and bridle start with a halter and bit-less briddle
You nomaly start training a horse when it is 5-8 months old. This depends on what you mean by training. If you mean basic training like ground manners that can begin right after the foal is born, However if you mean under saddle work you should never saddle any horse or pony under 2 years old, and it would be wise to wait until the horse was four years old before really beginning it's under saddle training.
3 years
A horse should not be ridden before the age of three. This is detrimental to the horse's health, and will cause severe problems in the future. The best time to start training a horse under saddle is when the horse reaches the age of four, when the joints of the animal have properly set.
you start with the girth, or the thing that wraps around the horse's belly so that the saddle doesn't slip off. you unbuckle that. then you slip the saddle off. tada!!
A handmade saddle takes about 10 days from start to finish for an experienced saddle maker. A saddle maker can work on several saddles at once because there are some stages when it has to dry for a long period of time before the next step can be taken.
when your horse is ready, if the horse is green broke at 4, then give them a year, and you should never start backing a horse (training to saddle) before the age of 3 b/c they haven't developed enough
It sounds like you may have a 'youth' saddle. A pony saddle is pretty small and you would be able to tell right away that it was meant for ponies. A youth saddle is meant for that in-between stage when the rider has outgrown a pony saddle and is still to small for a full sized horse saddle. To find out you can measure the saddle's tree. Take a tape measure and start at the pommel and run the tape to the cantle. This will give you an idea of the size of the tree which is what the entire saddle is based on.
You shouldn't really because they are not fully grown and will have problems in the future if backed to early, the average age is around 3-4 years old. Although you shouldn't ride a horse before 2 years old you can get it used to having a saddle and girth on it during it's yearling year by using a lunging surcingle and a saddle pad. You can long line the horse to get it used to the bit commands and that way it won't be as hard on the horse when it's saddle training really begins at 2+ years old.
When you tack up, its mostly the same as if you were tacking up your horse any day. Start by grooming, then the saddle pad, then the saddle or show saddle. then, put on the bridle or show bridle, and then your all set. To mount, put your left leg in the sturrup, face the rear end of your horse, and carefully swing your right leg over his hind quarters, and sit deep in the saddle. pick up your reins, sit up, heels down, and enjoy the ride!