1 Timothy 2:12 says this 

"But I suffer not a woman to teach, nor to use authority over the man: but to be in silence."

I know that dominican nuns have been allowed to teach but at what age are males not able to be taught by them? Society considers 18 to be an adult. But I wonder what God considers to be a man. I can understand a nun teaching 1st graders but at what age does it stop being permissible  male to be taught by a woman?

I think we need to be prudential. Isabella led an army. If she didn't do her part a part of Spain would be ruled by Muslims.   

Not allowed?  I think the verse refers to teaching on spiritual matters, in the context of proper position in the Church.  My father just took an on-line class taught by a female for the physically disabled to make basic meals.  Given the topic, it seemed perfectly natural for a woman to teach.  
If you are talking about teaching catechism, then I’d think Confirmation preparation would be an appropriate time to separate the sexes.  Let male teachers prepare the boys for Catholic manhood, the female teachers prepare the girls to be Catholic women.  
If speaking of academic teaching in school, the time of puberty should be the dividing line.  Separating boys and girls should begin in middle school, grades 6-8, and be the norm for the high school grades.  
From a strictly pedagogical point of view, it is certain that boys and girls learn differently, and if possible, all but the youngest, grades K-2 or 3 should be taught separately.  

Yeah I think the verse refers to teaching in a way like the Church teaches, i.e with authority. Letting a woman show you how to do something, or tell you about a topic, isn't teaching in this context. It's women having authority over adult men that's the issue, which lines up with how secondary schools were traditionally split by gender and no young man would've had female teachers anymore after that.

Correct:

St Thomas Aquinas says this biblical injunction is relative to female exclusion from holy orders, and the exercise of authority in the Church, not to women teaching men generally:

https://www.newadvent.org/summa/5039.htm

Quote from: poche on Yesterday at 11:53:49 PM

Quote

I think we need to be prudential. Isabella led an army. If she didn't do her part a part of Spain would be ruled by Muslims.  

Why change the subject?

If she led the army, of course she was teaching men. Same with St. Joan of Arc. But they were leading and speaking to (teaching) men in a setting that was not overtly religious.