I wouldn't be too worried about flexibility, Remon. I used to study Kuk Sool Won (which is also Korean and shares many kicking techniques similar to Taekwondo.)

I found that what really help get my balance and flexibility where I wanted was strength training. Simply being limber enough to kick high isn't as satisfying or as good as having the strength to pick your leg up to the same height and kick in a controlled manner due to proper muscle development.

It'll all come with time and training (which my lazy ass as neither of anymore! )