It's totally possible with Nifi!
There are a number of ways you could go about it, and it depends on if you think the dates will have the same format, or if they will vary. (ie: mm/dd/yyyy or dd-mm-yyyy)
I found another useful conversation here that covers using the routeOnContent or routeOnText processors to evaluate a regex expression, checking if the value matches what you expect.
I would recommend looking at the documentation on those processors, as well as testing out your regex expression on a site like Regexr. Hope that gets you started!