i suppose it helps if you start earlier with flexibility, but when i started taekwondo i was very very inflexible, but aslong as you stretch regularly and properly (not going to start that argument again!) you can soon reach a decent level of flexibility.
after about a year i can almost do box splits, maybe another half a year ill be there, and have recently been able to perform those other sort of splits, you know the ones where you have one leg in front and one behind but only when im properly warmed up.
i was still a bit flexible from when i did gymnastics as a very young boy but you are younger than me so you should be able to become flexible enough to perform any kick or technique you would ever need to.


sorry i just read through that and realize its a bit of a mess, basically just work at it, anyone can increase their flexibility