There are loads of things to do.
Fates
Leves
Hunting log
Quests
Grind monster EXP chains
Dungeons
Edit: I'm sorry but I find it hard to believe you did all the (Non story related) lvl 20 quests and are only 21.
^_^'
There are other regions you can travel to in order to get more quests.
If you're really in a crunch for exp you can do Guild Hests that grant a boat of of exp for the 1st completion.