The first islands in the pvp side of the game begins at level 40. You can obtain xp scrolls from the first two islands up to level 120. Though; Iah will not let you level past, or access after level 90 and will drop 1 gem per monster killed. Shuy will drop 2 gems, so and so fourth for kando, duan and then Rue.
Kando/Nado
When you are fighting for Kando you will want to remember that everyone is basically geared like a max level player, but they have no health comparatively. Don't bother with the stronger players, take out the lower level players before too many of them stack up and kill you. Drop them like flys and they won't hold you down like a giant.
Duan is unique from the other islands because you only obtain "island gems" between 161 and 200. where at 160 you have nado, and at 161+ ghost castle contains level 300s. Rue, on the other hand is like an upgraded version of duan, and ghost castle is within your level bracket (hopefully).