It's highly recommended that you level up a character to 80 manually then using the boost on an alt. This is so that you learn important skills about the game, such as dodging and what your skills and traits do. That's a great place to start for builds for any classes and how you want to play them.
Keep the warrior and make a new class you think you might envoy. Level that one up normally and learn the game. Once you know the game basics, you'll have no problems learning warrior even if you skipped all training and tutorials. you could also try to craft one or simpy look for groups of any dungeon.
1) Lvl 80 is max lvl (If you are max lvl and have all available masteries in the current region finished, your exp go to spirit-shard acquisition)2) Exp now goes into Masteries.3) Masteries are different per Region. Tyria mastery (Pact-Mastery, e.g. auto-loot, ): core maps of the base game + LS2. Or5p3.