Can you raise your legs into headstand? I think that would be the best indicator if you are “ready” for it.
If you can’t kick-up or get your legs up, you are not ready. If you can’t support your weight with your neck off the floor, you are also not ready.
You need to be able to go up, and not have your head on the floor. If you can do this, you are ready to be in the pose.
basically, you will know when you are ready…when you are ready, you will be able to do the pose. I don’t think there are any other tricks to it than that.
If you aren’t sure if you can do these things without falling on your head, maybe attempt it with the help of some chairs, your yoga teacher, or one of those headstand contraptions. Which honestly, scared the life out of me and I have never used.
The other good indicator, would be to do this pose"
Sit at the wall in staph pose - with your back against the wall. See how far your feet are from the wall in this position. Now…move so that you are facing the opposite direction, with your hands the distance from the wall your feet were.
Interlock your hands, tuck your head, and prepare to go up into headstand…but instead of kicking/lifting your legs up - lift one and touch it to the wall behind you so your body is at a right angle to your feet. If your head isn’t resting on the ground and you are supporting yourself, lift the other foot to the wall.
You are in headstand, but your feet are resting on the wall giving you stability and taking some of the weight. If you can hold you head up here, you can give headstand a try…
Good luck!