As a young dragon ages, it has a larger need for food and must acquire larger prey and with greater frequency. In many cases this means expand its territory. Often times in its search it will cross the boundary into the territory of another dragon.
In the unfortunate event that the two meet, it is likely that a battle will follow, presumably to one dragons end. It is possible that the two dragons might be of the same litter and the fight will be quite even. But, in most cases it will be a younger dragon stumbling into an older dragons territory. This is the source of many juvenile dragon skulls. Many believe that fashioning the bones into jewelry will imbue the wearer with propensity for justice and honor.