> Depersoning people by age is no different than depersoning by race or gender.

Those aren't really comparable. If I have a "no black people" rule or a "no men" rule, some people are permanently excluded and some people are permanently included. Those rules each filter everybody into two permanent classes each that they can never leave.

A "no people under age X" or "no people over age X" rule does not do this. Yes, it does filter everyone in to one of two classes, but any given individual starts in one class and then after a set time switches to the other class.

>If I have a "no black people" rule or a "no men" rule, some people are permanently excluded and some people are permanently included.

The problem is bigotry is usually based on an immutable feature. While gender is becoming changeable to certain degrees, age and race are not, one can't de-age a person or change their race on a whim. Additionally, claiming that because someone's older disqualifies them from having a full vote in society opens the floodgate every other manner of depersoning seen in human history over the last 200-500 years.