"The Sahidic is probably the earliest of the [Coptic] translations,
and also has the greatest textual value. It came into existence no
later than the third century, since a copy of 1 Peter exists in a
manuscript from about the end of that century."
20th century Coptic scholar and New Testament translator George W. Horner gives a date closer to 188 CE, based on "the internal character of the Sahidic [version]," which, he says, "supplies confirmation of a date earlier than the third century."
Coptic scholar C. S. Malan said, "The Sahidic Version was made when Greek was a living language even in Egypt, possibly in the second century."
The Coptic Church gives the date of 200 A.D.
The Sahidic Coptic version is likely as old, and as valuable, as the more well-known Old Italian, Vulgate, and Syriac versions.