I think being an Entrepreneur is a lot of trial error, most important thing is you need is faith
I am also reading a lot to improve my skill over this summer
if need some help I wouldnt mind to share thought in some kind of Master Mind Group
I hope you have read most of those books, so we have about the same content to discuss and we dont have to start from Adam and Eve
Age doesnt matter in your venture but dedication, but personally I think 15 years is kind of old to be an "Entrepreuner" Warren Buffett or most people started at much younger age.
Since there is no school that teaches how to be an entrepreneur, but life, it basically just depends on if you give up or not.