The only way to become a Gunner is through combat, constant combat! You must go challenge powerful monsters to experience the energy of the sky in combat.
Go to the Night Pirate's Camp in the northeast of the Prism Island Prairie and challenge a Night Pirate Guard, Night Pirate Vanguard, and Night Pirate Crew there.
After that's done, go to the Schilling Village on the Prism Island Prairie and look for Sage Babama. He is waiting for you there.
Only he can break through your energy block and let you advance to become a Gunner.
Child, I believe you are ready to let yourself become an outstanding Gunner.
The road ahead will be difficult, but I have faith that you will prevail.