Adherence to values and pursuit of discipline

I am 15 and I am wondering whether it is too late for me to build discipline.

I have heard that discipline usually comes in in earlier childhood, and that most of the people have hard time building it later in life, hence I am wondering has anyone had such an experience, or has an advice to it?

I have tried to help myself by creating my own philosophy, but it was to no avail because I have trouble following my own philosophy, due to it lacking popularity, thus rendering it unimportant.

Thank you!