|...the ultimate source for horse enthusiasts|
When someone asks what age they should consider starting a horse, most often they are referring specifically to saddle work, in which case the average is around 2-4 years of age. I cannot stress enough the importance of analyzing your horse and comparing him to the above listed factors before assuming two or even three years of age is perfectly sufficient. If you push a horse too hard you can create some serious long-term injuries or problems, and it's far easier to overdo a young and not fully developed horse as it is a mature adult.
Let's take a closer look at the bulleted factors above:
The average age a horse fully matures, both mentally and physically, is 4-5 years. Although you can start a horse under saddle before 4 or 5 years of age, it's important to remember they are still developing at that age and therefore your training regimen must not be too severe for their developing bodies to handle.
To make things even more complex, you must know your breed. For example, Mountain Horses are often started under saddle as early as two years of age as they are sturdy horses on the whole. Arabians are known to be much slower developers, and as such starting an Arabian at two years of age may not be a good idea. Unless you are familiar with the development rate of your horse's breed I recommend asking breeders and trainers that specialize in your horse's breed about their thoughts and experiences.
Even amongst the same breed each horse is going to have a different rate of development – like us, they are all individuals! It's important that you consider your individual horse's conformation and development rather than the breed standard. I generally start a Mountain Horse around three years of age, but I owned one gelding who was remarkably tall and slender for the breed. When he was three years of age I still could not see starting him under saddle without risk of harm because he was still in the midst of a strong growth spurt and his joints would have been under too much pressure. One or two years later his build was fully developed and this big, elegant and marvelous gelding was ready to go.
Whereas it may be safe to start a horse as early as two years of age, you must reasonably moderate the demands you are about to place on the developing horse. One hour of riding work may be just fine for a fully developed horse, but it is most often unacceptable for a two-year old. I advise to keeping your sessions with a younger horse to 10-15 minutes initially and working your way up slowly to even 15-30 minutes.
Keeping track of the duration of your training regimen is only part of the demands to keep in mind; equally important is the type of training you will request. Try to keep young horses to an easy, smooth and slow walk for most, if not all, of the training sessions since a trot or canter places much more stress on their developing bones and tendons.
Finally, the atmosphere you work your horse in can also place demands on him. Try not to work your young horse in a ring that has a deep layer of soft sand. While our normal instinct may shout, "Soft is good and more is better!" (after all, we love plush beds, comfortable shoes, etc.), it can work as a liability for a young horse since he must work harder to clear his feet from the sand, thereby placing more stress on his joints. Also important is to make sure your riding area is nice and level – uphill and downhill work will place more stress on a horse.
Even a fully developed horse will have a difficult time bearing too heavy a load for extended periods of work under harsh demands, so you can imagine we must be even more careful when working with a young and developing horse. When introducing a young horse to saddle work for the first time it is best to use a child, teenager or lighter woman as his rider. The weight of the rider becomes less important as a horse ages and develops.
Sometimes I've noticed people place too much importance on weight alone, though, since far more important than a rider's weight is a rider's balance and riding proficiency. An unbalanced 150-pound individual will place far more stress on a young horse than a balanced 190-pound rider! If a rider's weight shifts and weaves the horse must try to compensate to maintain his own balance… and it is this far more than the actual weight that can harm their bones and joints.
If you are confident enough to try riding bareback that will definitely cut a lot of weight off the horse's back – often in excess of 40 pounds depending on the material and style of a saddle! Those who wish to minimize saddle weight while maintaining the security of a saddle could consider an English or similar style saddle.
The above is only a crash course in what age a horse should be started under saddle. Before riding your horse for the first time (assuming the horse is not mostly developed already) you should be at least somewhat familiar with bone remodeling, safe and gradual training progression techniques, and warning signs that you may be pushing your young horse too far. Placing too much stress on a young horse can be disastrous as the Thoroughbred racing industry shows, but there are benefits that can be gained from starting a horse young… provided you are patient, caring and knowledgeable enough to do things properly.