3 years

By the time, a horse is two it will be almost completely grown so if your horse is 14.2 hands you may get another inch out of him. They will continue to fill out over the next two years, but I have had horses in the past grow a hand after two, but this is not the norm, so concidering what I know it would be safer to say by four years of age,

there is no actual certain year it depends how fast the horse grows and what breed but usually about 3 horse years

Horses are generally considered to have reached their full height by the age of 5 years with 80-90% of their finally height achieved at 3 years. While genetics play a role, it is possible to push growth through the use of high concentrate/protein diets (or stunt growth through malnutrition). Pushing growth is popular in the racing and show industries (the younger, the bigger, the better, the more money they can make), but this is not recommended by the majority of the veterinary community. Pushing growth comes at a price as the horse is more prone to musculoskeletal or neurologic ("wobblers") diseases because the body is forced to "cut corners" to keep up. Also, the high concentrate diet can lead to life threatening colic and laminitis. In fact, unless the horse is in intense training, such as racing (track, not barrel), a good quality grass hay diet is all that is required. Supplements should be resticted to correcting nutritional deficiencies such as Ca:P mismatch (important in growing horses), micromineral deficiencies (e.g. selenium in some areas), etc. If you find you need extra calories to maintain weight, you can add concentrates or a concentrate/fat combination (fat=corn oil or bran). Your veterinarian or county extension agent should be able to help you create a diet appropriate for your horse. Finally, just because you slow down the horse's growth, the horse isn't going to be "stunted". It will just take a little longer and you'll have a healthier, more solid horse in the end.

Ponies and draft horses develop slower so I'd say about 4. Tbs should be at their full height at two years of age. The picture is of a yearling by Montjeu, whom I had a share in untill he was sold at Tatersalls for 100,000 guineas. He is pretty much his full height.

usually a horse has reached it's full height at 3, and then from 3 to 6 it starts "filling out"... some horses mature faster, others slower, so it all depends...

Most horses, depending on the breed, mature to their full height at around 3 or 4 years old. Quarter Horses don't mature until around 5.

all the years of breeding different breeds of horses the average they reach full height is 5 years all the horses i have grown an inch a year from 3/to 5 there is a fact of measuring horses to there exact height and its worked for me more than a 100 times

The USEF doeant quit measureing ponies or horses until they are 6 years old. I had a Belgian/ Quarter horse cross that went from 15.3 hands at 3 yrs old, to 17 hands at 4 years old, so it really depends on the breed as to how MUCH growing they will do, as draft and warmbloods are extremely slow growers and do not fully mature to their final height until they are 6 years old. Lighter breeds may grow an inch easily between 2 and 3 and then posibly another inch between 3 and 6.

i have a welsh cob and she is 14.2 i have been told she will stop growing at the age of six , does lungeing make a horse look bigger.

Usually by 3-4 they have grown as tall as they will get.

On average horses/ponnies stop growing when they are 5. There bone structure isnt fully formed untill they are 5.