Basically what I need to do, is - stretch my lower back so that when I perform lotus position with chest on ground, my butt doesn't lift from the surface (it does now). I need to be flat with it. I have very good flexibility, but I haven't stretched the lower back because I am not sure if in the age of 18 it would be healthy for me to start doing it. I may not learn to bend my legs over my head from backwards, but I might learn to raise my lotus from headstand because now my lower back isn't streched and doesn't let me raise the legs. I will start training it slowly, unless there are any possibilities of back injury or maybe I am too old and can harm myself or see the negative effects in the future. I think so because many people complain about back pain in that area, and maybe it would not be so smart to start streching that area in my age. I also heard that the acrobats train it from young age, when their muscles aren't formed yet. If it's possible but heard, yet safe - I'll do it. If it can harm me - I won't. So please people tell me more information about this strech.
Thank you.