I think I beated Astos at lvl 10 or 9. Perhaps 8, I don't remember correctly. I stopped playing like months ago, but I just restarted.

Well, If I got those lvls, it was because I first went to the castle of ordeals to get the Zeus Gauntlet. I tried the Volcano at lvl 16, but the lack of attack power made the dungeon impossible. The Monsters didn't killed me, my buffs helped, but I just dealt 1 dmg with the Silver Hammers. It was... impossible. Maybe that's why I got so many lvls.

I also didn't beat the dungeon in the first try. I went once to get all the treasures I could. Then I went back to the inn, rested, went again to get more treasures and so on. Until I grabbed everything and I went Versus Kary. ...I needed money for the Magic!

I think that + the Castle gave me a lot of lvls.