I distinctly recall that Elio & Linda stated in one of their analysis videos that the Battle Beneath the Gods Eye was the first time that dragon clashed with dragon since before the Doom of Valyria (i.e. the other four who died on Dragonstone didn't die fighting each other). Unfortunately I can't remember the specific video in order to formally cite it.--The Dragon Demands (talk) 19:42, 6 October 2017 (UTC)
Date of birth
I've removed the statement that Quicksilver was born in 7 AC as I must say that the text remains vague about it.
The Sons of the Dragon discusses Aenys's health in the paragraph discussing his birth, ending with the fact that his poor health sparked rumors about Aenys being Rhaenys's bastard instead of Aegon's son, and with the fact that these rumors ended only after Aenys bonded with Quicksilver. Yet next, we also read that Aenys deteriorated when he was three years old, when Rhaenys died. However, it is not stated that Aenys deteriorated after having been given Quicksilver.
In fact, The World of Ice & Fire tells us that "But though his father and brother, Maegor (who was Visenya's child), were both warriors born, Aenys was made of different stuff. He had begun life as a weak and sickly infant and remained so throughout his earliest years. Rumors abounded that this could be no true son of Aegon the Conqueror, who had been a warrior without peer. In fact, it was well-known that Queen Rhaenys delighted in handsome singers and witty mummers; perhaps one of these might have fathered the child. But the rumors dampened and eventually died when the sickly child was given a young hatchling who was named Quicksilver. And as the dragon grew, so too did Aenys." Especially the bolded part implies that Quicksilver was actually born a few years after Aenys's birth, as he "remained [a weak and sickly infant] throughout his earliest years". Only after been given Quicksilver, did the sickly child thrive.
So the sentence from The Sons of the Dragon (which I think that the 7 AC was based on), "And the prince was slow to grow as well. Not until he was given the young dragon Quicksilver, a hatchling born that year on Dragonstone, did Aenys Targaryen begin to thrive." is not saying that Quicksilver was born the same year as Aenys was born. All it says is that Quicksilver was given to Aenys in the same year that his egg hatched (which says nothing about how old Aenys was at the time).