grammatical explanation

In a situation like the one in your sentences, i.e. when discussing a hypothetical event in the past, and its imagined later consequences, also in the past, the tense in the 'if' clause is the past perfect, and the tense in the main clause is the perfect conditional: if you had worked harder, you would have passed the exam. Thus the first sentence is the correct one.

If you were born a century ago, you're probably dead.

At 87 now Cen, well, almost !
But mebbe am already, just not conscious of it

I know the feeling.

So Cen welcome to The Club