Dragons naturally live much longer than normal Ponies or for that matter synthetic Alicorn Princesses. Spike never took Twilight's death well so Celestia and Luna took the kid under their wing. They also took in Discord or maybe Discord just invited himself in, either way Spikes moody teenage ways leave the three elder members of this little family confused and wondering how the hell one raises a teenage dragon. These are the awkward encounters one teenage dragon has with his Guardians and the spirit of chaos while living in Canterlot castle.
Note: This story takes place in a universe in which equestria is an island nation on earth.