Let's take a first conditional sentence, expressing a real possibility:
If I do my homework, I can go out.
How to express the same real possibility in the past? If I simply change it to the past tense, it becomes a second conditional sentence:
If I did my homework, I could go out.
As far as I understand, it expresses an unreal or improbable possibility in the present. I want to express a real and probable possibility in the past (as in, "At the time when I was a teenager, if I ..."). How to do it?