Rewriting

[allthewayanime]

Would it be correct if I rewrite this sentence ' I haven't met James for 3 years' as:

'I last met James 3 years ago'
'The last time I met James was 3 year ago'
'It's 3 years since I last met James'

[Barb_D]

All are a problem. You meet someone once, and after that, you have met them.
If you want to do this as "see" then:

I haven't seen James in three years.
I last saw James three years ago.
It's been three years since I last saw James.

[allthewayanime]

Is there a difference if I say 'it's 3 years since...' instead of 'it's been 3 years since..'?

[Barb_D]

In my opinion, "It's three years" is not grammatical. You need "It's been."

[emsr2d2]

You could say "I haven't met up with James for three years" or "It's been three years since I [last] met up with James".

"To meet up" is not the same as "to meet" in this context.

[Tdol]

In my opinion, "It's three years" is not grammatical. You need "It's been."

I get the point about the grammar, but it sounds OK to me and I must confess that I use it.