It seems that general developmental questions ("at what age should a child be able to do X") are on-topic.
It's also clear that specific medical advice is off-topic ("My child has this and that symptom, what is his illness").
However, I could not find a rule for questions that are a blend of the two:
"At what age is there a cutoff between a certain symptom being 'normal for the age' vs 'abnormal enough for the age that you should see a doctor about it'
(my specific example is bedwetting).
The main distinguishing characteristic of this kind of question is that while an expert level knowledge would be useful in answering it, it is not required - most of the time, the answer can be found by browsing Cochrane or well established medical info repositories or research.