[vince89]

Its more technique than flexiblity imo. I know people who are flexible as shit (like Yoga type people) but I doubt they could even kick me to the torso let alone the head.

You have to launch the leg and go for it, this is hard because it feels like you'll fall on your ass if you go for it but you'll get used to it. Also another thing that gets my high kicks higher is doing a little skip before the kick but I dont recommend doing this in sparring.