Lol @ everyone screwing up the 13 year difference
I just read in one comment, "even if they got back together, she would be too old to have kids" - Are you serious???
Jack is 36 and Kate is 34 in both scenarios and it happens in the same year, in the glimpse life Annie is 6 (IRL - possibly even younger portrayal in the film ((for all characters))) and the son had just been born.
So when they get back together it would be nothing for them to pop out a couple kids, even 6 years apart.