Societal expectations regarding required milestones in your life, and when you should achieve them. Nothing more, nothing less.
There aren't so many of them now, I think. Or they're not as strong. For instance, I don't think it was a coincidence that it was your Nan (i.e. someone of an older generation) who expressed her expectations like that.
I guess it is harder for us NDs as we do tend to reach these milestones later than NTs do (if we do at all). But thankfully, as I said, there's less societal expectation than there used to be in the past.
We NDs forge our own paths. On the flip side, for example, I've heard of people getting together as a couple before they were really ready (because of said expectations, etc). Societal expectations can be toxic for that reason.
_________________
I may not fit in everywhere, but where it counts, I belong.