All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If the conditions of marriage (getting married with the consent of the guardian and in the presence of witnesses) are met, then the marriage is valid. As regards the guardian of a new Muslimah if she does not have a Muslim guardian, read the following Fatwa: 83373 and 83338.
A man's marriage without the consent of his parents is valid as their disapproval does not have any affect on the validity of the marriage. However, it was better for this man to consult his parents regarding his marriage lest he would hurt their feelings and avoid causing harm to them. Since the marriage is now completed and the woman is religious and of noble character, the marriage is legally valid. So, if there is no legal reason for divorce, then he has to keep her as a wife and should try his best to please his parents using all the possible and lawful means and being kind to them.
Know that the age difference has nothing to do in marriage as the Prophet married Khadeejah while she was much older than he.
Allaah knows best.