From Reply No. 24, "ABOUT MARCION," on the "First Century GT origins" thread:

Marcion was the first to propose a New Testament canon. His canon consisted of only eleven books grouped into two sections: the Evangelikon, being a version of the Gospel of Luke, and the Apostolikon, a selection of ten letters of Paul the Apostle who Marcion considered the correct interpreter and transmitter of Jesus' teachings.

Marcion's dates being ca. 85-160 C.E., this also makes those letters first-century works.

P.

“What I admire is honesty and truth, no matter who, or what, the sources are.”
— Uri Yosef