When can you determine the gender of a clothed baby or toddler - What age specifically?

When we had our twins, a boy and a girl, we resisted the expectation that the boy wear blue and the girl wear pink. On occasion we deliberately switched the colors and the effect was hilarious. It was a proof that in most cases people can’t determine the gender of a 3-month-old baby when clothed. The ability to tell the genders apart comes later. When exactly? Not sure.