My studio won't let students invert until they've been poling for 4 months. They just won't teach it until then. I learned it, but I wasn't ready. This particular instructor taught us to kick into it. Big no no! Other instructors at the studio would have told me to wait. I could DO it, but only with kicking and with poor form. Needless to say, I ended up straining my intercostal muscles. I had torn them in college and to feel that pain again was something I had hoped would never happen. The intercostal muscles are the vertical ones between your ribs that expand when you breathe. The pain was horrible and affected that whole side of my body. Even lifting my left arm (which would stretch my ribs) was hard, and I certainly couldn't put any weight on it for a spin. So, then I became lopsided. Even though I stopped working on inverts to do it right, I was forced to do everything on the right arm! I am still struggling with strength. Worst of all, I used to be fairly balanced in my spins, right and left. Now, I struggle with spins to the left after having to wait for those muscles to heal.
It's really not worth it to invert too early. I'm waiting until it's right. I'll do one every now and then, but only one and I do my best not to kick (even though I still do), and it's not an exception I often make. The injuries from inverting too early have held me back even more and even stunted my progression. Don't give up and keep working toward it (safely), but don't let yourself compromise your health for this accomplishment. It's not worth it!