A collection of pdfs etc for reference.
A paper about Afro Asiatic and inparticular Chadic. From the paper…
Chadic is clearly the most intemally diversified subgroup of Afroasiatic and perhaps for that reason might be considered as the most ancient branching. However. linguistic geography suggests rather strongly that it is indeed an intrusive group reaching the region after the establishment of the Nilo-Saharan and Niger-Congo phyla (see maps in Perrot 1988; Crozier & Blench 1992; Blench 1993a, 1997a). Since its nearest relatives are geographically remote (Berber or Cushitic) it has often been suggested that speakers of the Proto-Chadic were mobile pastoralists of some type.
Of passing interest is that these Chadic speakers (like the Ouldeme and Hausa) can show exceptionally high levels of R1b, a Y chromsome derived from Eurasia, probably a trace back to the neolithic pastoralists from West Asia/Asia minor.
Having done a little quick reading on Chadic, it seems to have proto words for goat and sheep which would take it into the Neolithic for dating. Other sources I have place as a relative of Berber languages, not some ancient branch that’s been evolving in isolation for aeons.