I think this phrase was invented and became handy to advice someone to act foolish. For example, what a child in the age bracket of 2 to 3 does is charming and is representative of child's innocence. But if a grown child of say 12 to 14 years adopts similar gesture to get himself a toy or a permission to go out would look not so funny.
Similarly, if a teenager son of a "very highly placed in society" father orders around his father's juniors - it would look out of place.
I have also seen some elderly ladies competing with teenagers in certain things which does not befit their age.
In other words, the grace is lost!