Board Thread:Questions and Answers/@comment-27189333-20151111140253/@comment-24577221-20151111153956

The island becomes available when you buy Air Island, regardless of the player level. But if you want to do anything there, you need a Shugabush monster there. You get one there either by buying one there, or by breeding one on Plant Island, feeding it up to monster level 15, and teleporting it to the island.

It's unfortunate that the word "level" is used both for player level and monster level -- it's confusing. Dungeons and Dragons has/had the same problem.