In terms of Athanasius scholarship, this homily isn't considered one of the authentic works. Its current designation in Clavis Patrum Graecorum is 2187, which is within the range for "dubious" works attributed to Athanasius.
"Dormition et assomption de Marie : Histoire des traditions anciennes" (1995), by Simon Claude Mimouni part of the Beauchesne collection on theological history, summarizes the discussion of the work this way, in footnote 230 on page 416
As to our question, Mimouni explains that the current scholarly view is that: "Il est difficile de considérer l'attribution comme authentique." (It is difficult to consider the attribution to be genuine.) Robert Caro's suggestion is that the author may be Didymus the Blind (late 4th century).
It may indeed be from the 4th or 5th century (as Caro thinks). The bottom line, however, is that this is not one of the authentic works of Athanasius.
From the standpoint of historical theology, keep in mind that the veneration of Mary is something that grew over time. It is not an apostolic tradition, nor does Scripture teach us to venerate Mary in the sense that Roman Catholics and Eastern Orthodox ask us to do. We can describe her as being blessed by God in the sense that Scripture says, and we can also affirm her apparent role as one of Luke's eyewitnesses for the Gospel of Luke. That said, the cult of Mary is entirely inappropriate.