I was the same initially. I got it to 11 and got bored. Then went to 16 when a friend asked if I had a lvl 11 job for astral burn pt. I didn't go too well as the tank got stuck healing so we lost half the mobs lol.

So I sat at 16 for ages, tossing out Mavi seals left right and centre as it was my only job under 30. Then for some reason I got the urge to go spell hunting. I think just to get away from the abyssea way of exping. I'm now 63 and got most of my exp from just farming spells. Occasionally when I cap skill and have no more spells that I can learn I'll join a book burn and get a couple of levels then go off hunting again.