How long does it take to get pretty good at gymnastics?

I am 13 and I have been doing gymnastics for about 3 or 4 years. I don't do competitive but I kind of want to. Some of my skills include roundoff 2 back hand springs, kips, fly aways, front tucks, back walkovers on beam and front handsprings on vault. I am very flexible and can do over splits on both of my legs. I want to be at about a level 6 when if I start doing gymnastics competitively. I know its different for different people, but how long do you think it will take? And can you recommend any conditioning to make me a lot stronger really fast???