I'm running SkyDemon plan 3.13.1.0 on a fresh install of Windows 10. When accessing Pilot Notes for an airfield, I get the following (approximate) error message:

Yes, the threshold is currently two years. If there is something ongoing and important to know about an airfield, would it not be reasonable to expect it to be re-posted at least once every two years?

I disagree. Imagine an airfield, eg in the french province, where two pilots/year are posting pireps. Every second of these posts describes infrastructure. Every fourth of them describes the transport from/to the airfield. Tricky wind conditions are described only every two years etc.

Have a look at eddh.de. You may grasp the meaning even if the posts are in german.
https://www.eddh.de/info/pireps-all-std.php
Some of the reports are more than five years old and still helpful. If it is ever necessary to limit the timespan reports are displayed, I would advocate for 5 ore 4 years.

Alternatively, you could limit the number of posts displayed regardless of age, e.g. to 8-10 posts. That's enough to get an overview.

Or not, if most entries are along the lines of ‘Lovely airfield, will come back’.