Dragon Riders are dragons and humans that share a bond, a special bond, a bond that binds one another to each individuals soul. The dragon and the human see and treat one another like equals, and each relies on the other to protect and guide them through many fierce battles. If something was to happen to the rider, the dragon had to help them in any way. Same for the rider with the dragon. They are both partners, and must treat each other like partners to the bitter end.
The rider's age varies from teenagers to adults, but never to pre-teen, or child, since it takes an effort to earn a dragon's trust. When a bond is created, nothing can break it.
Before the bond is created, rider and dragon must train and hang around one another till each has earned the others trust. Then, comes the harder part, coordination. If a rider is out of sync with its dragon, or the dragon won't heed its rider, then the bond is not strong. Both rider and dragon must obtain an understanding of one another in order to work together as one.
There are riders and dragons, that don't see eye to eye, riders that abuse their dragons, and dragons that loathe their riders. These riders do not understand the power of the bond between rider and dragon, and misuse their dragons as tools and pets. They are not real riders.
Dragons exist all around us, many that we can't even see, yet we know of their prescience. Many dragons are wary of humans and stay away from them, while others go towards humans.
Dragons have many means of communication, some of them human speech, body language, and facial expressions. The relationship between a rider and his/her dragon includes that both must understand the wishes of the other, and trust each other. If neither understands, then there is no bond between them.
Most dragon riders are recruited for missions in their country/kingdom. Some work for kings and queens, leading their armies to battle or hunting down a traitor, and sometimes protecting the land in general. Other times, the situation is different. Sometimes a young teenager is chosen to become a dragon rider and is paired with a dragon. This team is then used to protect the land from evil tyrants, wizards, kings, etc.