The correct answer is “an impediment caused by his physical limitations”. He is worried because he has not accomplished what he should have as a grown man of 23. This octave shows that he is trapped between maturing and growing. The main concern of the speaker is that time took away his young years and hasn't given him enough time to achieve anything important in his life, and his body is accompanying this process of no growing that’s why he feels limited.
I would go with A. worried.To me, Milton seems worried because he hasn't yet created a great body of work, and he is 23 already. He feels that he should have created something important by that moment, and he is worried that his life is passing by without him accomplishing anything.
