The Dragon Age was a dark period of the Land of Stories history. Lands were ruled by tyrant kings and evil sorcerers and tormented by dragons. According to the Timeline Chart from A Grimm Warning, the Dragon Age lasts roughly from the Middle Ages to the end of the Renaissance in Our World (5th-17th century), though time still moved a lot slower in the Land of Stories before Alex and Conner were born.
The Fairy Godmother discovered the existence of Our World during the Dragon Age, and recruited Mother Goose and the other fairies to help her spread her stories some time between the Dragon Age and the Age of Magic.
The Dragon Age ended when fairies and elves banded together and killed the dragons.
In the following time, called the Age of Magic, the fairies formed the Fairy Council and founded the Happily Ever After Assembly. In A Grimm Warning, the Masked Man explains to General Marquis why the fairies have ruled over the Land of Stories since then- it would take a dragon to challenge them.