My 15 month old DD says yes (yeah) in context all the time. She doesn't say the word 'no' though. She has said 'no' a few times but not for at least 2 months or so.
Her vocabulary is probably about 25-30 spoken words I think. I've not counted recently.
I've read that 'no' usually comes way before 'yes' so was wondering if anyone else had this.
The fact that she doesn't say no sadly doesn't mean she's unusually compliant. She tends to shake her head or shout instead.