You don’t need to be Level 60 to start leveling in the Dragon Isles!
The introductory quest “The Dragon Isles Await” is available even to Level 58 characters! If you decide to level up a Level 58 character, keep in mind you’ll have to complete more side quests or dungeons to reach Level 70. The main campaign is currently gated behind player level and requires 66 in Azure Span, and the final two chapters in Thaldraszus require max level.