Here is the official answer. I need to research the subscriptins mentioned, because I also have learned it to be much later.
*** si p. 176 par. 6 Bible Book Number 40—Matthew ***
6 Matthew wrote his account in Palestine. The exact year is not known, but subscriptions at the end of some manuscripts (all later than the tenth century C.E.) say that it was 41 C.E. There is evidence to indicate that Matthew originally wrote his Gospel in the popular Hebrew of the time and later translated it into Greek. In his work De viris inlustribus (Concerning Illustrious Men), chapter III, Jerome says: “Matthew, who is also Levi, and who from a publican came to be an apostle, first of all composed a Gospel of Christ in Judaea in the Hebrew language and characters for the benefit of those of the circumcision who had believed.” Jerome adds that the Hebrew text of this Gospel was preserved in his day (fourth and fifth centuries C.E.) in the library that Pamphilus had collected in Caesarea.