Do people in Britain use this structure nowdays? Or is it considered archaic there? [closed]

Solution 1:

Yes, that is a normal construction to me.

It is effectively the past of If I were a boy.

If I were a boy, I would roam... is a counterfactual in the present. If I had been a boy, I would have roamed... is counterfactual in the past.

Just as with past perfects in general, it is optional when the temporal relationships are clear without it, and I suspect that some people would use it less than others.

I also find the mixed form If I were a boy, I would have roamed... to be natural: the past infinitive in the apodosis makes the time clear, so the past perfect in the protasis is optional.