I was around 15 when I first wanted to compete in an Olympics. I even remember the first time I got to wear a GB kit as a junior. I've even kept it. It's in my mum's loft somewhere, probably gone mouldy by now.
Even if you're improvising, the fact that beforehand you know certain things will work helps you make those improvisations successful. It really helps to have a certain amount of knowledge about musical structure.