I think it has a lot to do with how each of us are raised, but as a child, getting told to 'grow up' or when you grow up... along with concepts like don't talk to strangers alone etc., creates this subtle perception of an age transition. I've come to view that bias as a subtle prejudice in a way. I think it is a common fallacy most humans around me seem to posses but seem largely unaware that it exists.

This age bias is at the heart of a lack of value placed on the young and many social expectations. It could even be a major factor in why population decline is happening in the west.

Someone wrote recently that academia is largely about forming good ideas at a young age, then spending decades trying to prove their merits and defend them. As a society we undervalue the best ideas of youth, we do not value youth or respect their autonomy and fundamental needs to thrive.

I find that funny, because I am only wearing a mask of age and am fully aware that I am still the same curious child at heart. I kept waiting for the day I would feel all growed up but that day never came, and I live my life blindly doing the best I can with the opportunities I have available.