i guess what ur teacher meant is if u want to learn chinese at a native level u need to start as early as u can, that is not wrong. cos the core of a language is the culture( i mean the inner feelings in ur heart), a child could accept it naturally, but when u grow up, even only teenager, u already has ur opinion of world and life, then the way u learn a foreign language is different from children's.
but anyway u can learn things in any age, as long as u want to. and u r still quite young, at the age people have good memory and energy, therefore better possibility to learn new languages well.
trust yourself, no need to feel upset just for what ur teacher said, nothing is impossible. :)