from a chinuch perspective. the beis yackov (type) school my daughter goes to requires the girls to wear appropriate sleeve length after pesach of the pre-1a year. this is when most girls are between 5 and 6. it is to get them used to wearing appropriate sleeve lengths when they must (so says the school letter home). what the actual halacha is, i dont know, but clearly this school does not believe it is 3.
can someone provide a source for the “chofetz chaim”?
tx