You're last post says you shouldn't care if they use the washroom corresponding to their gender.

The guy is open about it - he hasn't had bottom surgery so he still has a vagina while the girl is only sixteen so she's too young to have had surgery.

But what exactly is a "male physique" or a "female physique".

So how will you know whether someone is trans or not?  After all, we've seen any number of cases of women (born as women) being challenged in washrooms because someone doesn't think they look feminine enough - too tall, deep voice, short hair, mannish dress, whatever.  So how do you tell?