My daughter is a month older and she’s pretty similar in terms of yes/no. She just says “no no” and shakes her head pretty often.
She may just be trying out vowels and consonants and seeing how they sound. For an information.... There is an autism screening at the next big visit, the 18 months
Don’t be concerned stuttering is a normal part of development and it comes as toddlers start to learn more words everything sound like normal development I wouldn’t be concerned.
I think it's their way of practicing vowels. Mine does a a apple or the exact same thing with e e elmo or up up up high. Super smart, everything I've read says it's normal for them to be obsessed with something new for a week or two and drop it most likely when they learn something else to obsess over.
This sounds a lot like my girl who is just a month or less younger. Dunno if it’s normal but she’s not the only one. And exact same thing with Elmo!