Doug Shaver

I'm thinking they probably reached their current form in the early to middle second century. Earlier versions could have existed in the late first century.

I believe this mainly for two reasons. (1) It fits what I think (for many other reasons) is the likeliest scenario in which Jesus, in the minds of Christians, evolved from a mythical being to a historical personage. (2) Their existence is not unambiguously attested before the middle second century, and not by their purported authors' names until late in the century.