Flying mounts have become one of the most touchy subjects in the WoW community since they launched during the Burning Crusades. They’ve been a staple of every expansion since, though when they come out tend to vary.
Shadowlands will let you fly (apart from in the introduction quest) from level 50 onwards once you’ve unlocked it on one character. As always, this will vastly improve, and speed up the overall leveling experience in Shadowlands.