Levels four and five constructed. This is the level that start tinkering with all the engine and putting specifications the inside as all right. The higher the level you go, better work you realize you'll be putting to barefoot. All of the levels have some kind age prohibit. Yet, this is just how they think is suitable to begin to use the apparatus. It takes into account the fumes by way of glue, paint etc., the skill doing each level, and such. What it all comes down to though is the place where comfortable you feel with what you're doing. Some people get it just easily, genuinely fly by skill levels one and two