During adolescence, there is a surge of neuron development and synaptic connectivity. Basically, the brain is wide open to new leaning in adolescence. The application of this learning means that while specialized neuro connections are developed and strengthened, perhaps piano playing skills, the neuro connections that are not selected fade into lessened activity. Neuro connection spurts of activity during adolescence start at the back of the brain and move through to the front. So, in a sense it may be true to say you lose some potential for learning, that is only having gained masses of new potential for learning. The answer to this must reflect your textbook and your instructor's expectations though it may not reflect the most current results of brain research.