Anecdotally, I’m going with BiG don’t worry about. It won’t be an issue. My first B spent weeks at an Irvine animal shelter in California. Before that, who knows. He settled in wonderfully. Bonded with the whole family fast. Made himself at home fast. Wonderful dog. Spectacular relationship. Aside from the normal Basenjisms, no issues. We think he was between 4 and 6yp when we got him.
The second two, that I have now, where about 2yo when we got them. We know their entire history, which had always been with our breeder. Our male, who we got first, seemed a bit melancholy after a few months. Then we got our female. He adjusted quickly, but I also believe he would have been fine on his own given a bit more time. Both have very distinct personalities and behaviors. Our female is very much Basenji, maybe the most in terms of mannerisms, but oh does she love people. Super affectionate. She’s my sweetie. Our male has a big personality, can be a bit demanding, but he’s my buddy.
If you’re ready to invest the time, effort and energy that a Basenji requires… I don’t believe you’ll encounter an issue you can’t work through. IMO, Basenjis require a somewhat advanced level of dog experience. Two defiantly does. Rowdy little bugger, but dang they’re fun!