I had a discussion at work today about this, obviously there was the natural confusion that TW = male, however one of my colleagues is a "Rugby Mum" her son is built like the side of a brick shithouse and her daughter like a little whippet. She summed it up nicely by declaring "well that's a stupid idea".
Her son knocked someone unconscious recently, it was a perfectly legal tackle, but that was the consequence, she said even the difference between her son and daughter when he was her age is striking. We also discussed if even 11/12 was too old to be separating boys and girls.
Everyone agreed with her that it was a stupid idea.