User blog comment:TheCarrotSaysYumYum/Dragons, People and Demons.../@comment-171.98.99.216-20120722100129/@comment-4449950-20120722103546

The first DS's would have been taught aaaaages ago and have been known all around Fiore. Later, as Zeref seemed to have died off or disappeared (presumed dead by all people in the land) these trainings would have slowed too (with DS Magic becoming rarer and rarer). But then when demons (such as Deliora) kept appearing, some dragons (specifically Igneel, Grandeeney etc.) would have trained extra Mages. This would have happened not long before the start of the series, when Natsu, Gajeel and Wendy were children, and would have stopped when they disappeared. This is why DS's (like Natsu and Gajeel) are considered to be rare, because not many existed anymore... let alone ones so young.