Here's some Game of Thrones trivia (specifically on the dragons!):
The dragons' scales grow harder as they get older. This makes it harder for them to get injured. The thicker scales also provide more protection against flames and fire-breathing dragons.
Not everyone is able to ride a dragon. It is believed that those with Valyrian blood can become dragonriders, possibly because they made dragons with their magic or were the first to discover the dragons.
Dragons can sense when their riders are in trouble.