Present Perfect with “that”

Question

I came across the sentence "It's been thirty years since my parents first met." I am sure that if I heard "It's been thirty years that my parents first met", I would accept it as grammatical, but I can't find any reference to support this. Am I wrong?

Answer 1

You'd have to use present perfect on both sides for that sentence to work:

It's been thirty years that my parents have been married.

Otherwise, remove the present perfect from the first part:

It was thirty years ago that my parents first met.

In both examples, as well as the ones you referenced, that acts as a conjunction, or should. If you are trying to use it as a determiner, then it simply doesn't work there.

Answer 2

In your example, you would have to use the word since.

It's been thirty years since my parents first met.

Using since here is actually related to the span of time since the moment your parents met, rather than the first half of the sentence. Using that would be grammatically incorrect. However, you could say:

When I look back on my life, it's been thirty years that I wish I could forget.

In this instance, that is used to create a relative clause, connecting the thirty years to the last half of the sentence. You can do this with other things too:

I have eaten something that wasn't good for me.

This isn't restricted to the present perfect, either:

It's going to be thirty years that I wish I could forget.

But, as soon as you're talking about the span of time, you have to use since again.

I have eaten at least three kilograms of cheese since my parents first met.

I haven't eaten anything since yesterday.