I kind of wonder if a purely homeschooled, entirely isolated teenager would make them. I guess it would also result in a second Chris-Chan, so the experiment is worth doing.

It'd be better explained trough socio-linguistics than neuro-linguistics. Teens in my country dont make these sounds except for the glottal fricative 'uggggh' sighing sound. And I question whether all or any of these even existed in the U.S. 70+ years ago.

Voiced alveolar stop and breathy-voiced low-back unrounded vowel, with much advanced tongue root.

CCcckkk!