Determining your fitness level when it comes to crulsing is easy. You don't have to worry about if you are fit enough to start crulsing.
Whatever level of fitness you currently are at is where you always begin each time you practice crulsing. Anyone at any level of fitness can crulse.
Crulsing is a practice, not an exercise. It is a practice that you do what you can and eventually move toward what is possible.
So, if you practice crulsing, you are always at your current level and capability. So there is no need to worry about if you can do it.
Crulsing is about movement; you only focus on what you can currently move, not what you can't. So as long as you can move, you can crulse.
So get out there and move. Happy crulsing!