Tense question: "Is he walking yet?"

[abra]

Sadly, I have limited exposure to spoken English, so I can only come up with examples taken from books and dictionaries.
Here's a sentence from OALD (Oxford Advanced Learner's):
'Are they speaking to each other again yet?'

BTW, speaking about babies, what other 'stages' in their development would you refer to using the Present Continuous + yet? (as a substitute, it seems, for 'Can he/she do this or that yet?' or 'She can't feed herself yet')?
Can I ask you about your elder child, 'Is he/she reading yet?'
And, for that matter, could someone ask me about my big son (who will be 18 soon), 'Is he drinking beer yet?'