I've recently learned that genetically-speaking, the San, or Bushmen, are the oldest race of humans known. Does it follow that their language - the "click" language, is also the oldest? I understand that there are at least three dialects of Khoisan. Can one be identified as older than another?

There are about twenty or so Khoisan languages and probably many other dialects of those throughout southern Africa (link). It's the term click language I am having difficulty with. All of these languages do have click consonants in them, and if that's what is meant by click languages, then I understand you. But, it is important to remember that the Khoisan languages have , at best, only been recorded in the past century or so. We really do not have any evidence that the proto-Khoisan languages or whatever proceeded them had clicks. They might have and they mightn't have. Also, as Homo sapiens left Africa about 60K BP, it is unlikely that people were speaking anything back then that can be identified with modern-day Khoisan. 8-10K BP is about as far back as we can reliably reconstruct a language.) We have clicks in English, they are just not used as phonemes, but more as verbal gestures: e.g., the giddy-up lateral clicking sound made to get horse to go, the kissing click, the click usually transcribed as tsk, etc. Also, some other non-related African languages, e.g., some in the bantu family, have click consonants, too.

I guess I'd best start unlearning some stuff.

Thanks.