Anyway, I decided to check out this document I have never heard of and found a translation I can preview at Google Books.
https://books.google.com/books?id=I2g1z_oltV8C
I'm a few pages in, and the author is on a theological tangent about the speech of the Savior rather than anything specific to Jeremiah. And then, in Book I §8.5 he makes the odd statement that seems to be about the incarnation. (I am adding Scriptural citations in brackets.)
I find it kind of weird that the author is using Jeremiah as a source of information about the first words of Jesus. "I do not know how to speak, for I am a youth" is, after all, Jeremiah 1:6. And with its juxtaposition to the statement about the womb, the writer infers that these are the Savior's first words out of the womb.
I'm having difficulty understanding what "he has appeared later in life" means. I keep imagining the Marcionite view that Jesus just appeared in Galilee as an adult to begin his ministry, but maybe there's a more obvious explanation.