But your performance reviews don’t have anything to do with age, so I don’t see how that could be.

Any review that's not a hard metric can be gamed to be about anything the reviewer cares about.

They don't like your age and prefer some fresh face to pull with no family alnighters and work for half the money? The performance review will show you as lacking motivation or some such shit.

And any review that's based on hard metrics, can be manipulated by the reviewer just as well.