What if it were 5 brothers?

No, the parents wouldn't probably be as strict.

Cecilia's remark sums it up pretty accurately at the beginning of the film when the doctor says that she's too young to know how hard life can get. Her answer is, "have you ever been a 13 year old girl?"

There wouldn't have been any story.
Society - and certain families even more so - believes girls need to be sheltered and protected.
Girls don't openly pursue boys in quite the same way that boys pursue girls.
Boys aren't victims of madonna/whore profiling and don't suffer the same kind of shame after a one-night stand that girls do.
And all of the above points were even more true during the time that the story was set in than they are today.

Of course society punishes male expressions of sexuality. Men may not be "slut shamed". They just get lynched, like Emmett Till.

The parents would be just as strict, they are Catholic. I don't mean to generalize, but I have a friend who is Catholic, his parents are really strict, and he was taught to believe that making out before marriage is wrong. The strictest of Catholics are psycho.

That would be another movie, wouldn't it?

I smell a sequel.

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