You can't age a horse like you want by showing a picture of the horse wearing a bit...
We need to see the teeth.
Push the lips back and show from the side the teeth how they look touching each other.
Push the lip back and show the teeth from side and front, upper and lower teeth.
Watch your fingers and open the mouth and take a picture of the grinding surface of the teeth upper and lower jaw as clear as you can.
The horse is branded so is registered...did you not get registration papers?
Birth-date is clearly given on those papers...
This link might help you some or get those camera pictures and show them and the teeth gurus will be pretty close to aging correctly. Aging Horses by Their Teeth
By looks, to me he looks older than 13 with such a drop in his spine is often seen in senior citizens although horses who are not ridden or exercised building proper muscling can get a dropped back too...
Get those teeth pictures and post them so we can help you out.
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