Was my action correct in refraining from offering myself to a young man who proposed to me, and what is the extent of the validity of the fatwas that permit a woman to offer herself to a man whose religion and character she approves of?

This young man is a stranger to you, and his hint of admiration for you is impermissible. You did well not to reciprocate. If he had been desirous of marrying you, he should have approached your guardian. Do not grieve over missing the opportunity to marry him, for marriage is a provision from Allah. Entrust your matter to Allah and ask Him to ordain what is good for you. Seek help from your relatives in finding a righteous husband, for it is permissible in Islamic law for a woman to seek a righteous husband and to offer herself to someone she wishes to marry, even if shyness might prevent her from doing so. Do not burden yourself with thoughts of him marrying someone else, and if your heart has become attached to him, there is a cure for such infatuation.