"Searched" this question and there are numerous Articles of folks offering their "opinions" with their "justifications" for their determinations of when the Gospel of Matthew was written/and by whom.
It varies from 50AD to 100AD, and each seems to have their own "set of circumstances" and "evidence" for their assertion........
Not to discount this Thread, nor to speak against it's Author, BUT, IMO, when the Gospel was written is not nearly as important as it BEING written, and being the Inspired Word of God.