Just like 16 years old people can’t vote because too young, 80+ years old people should not be able to vote, most of them are too distant from everyday reality of younger people to be able to take a wise decision for the community and also often stick with (way too) old ideals from their years
Think of it like this: voting is like bodily autonomy.
While it’s reasonable to not demand newborns give verbal consent before being picked up and fed, a twelve year old is definitely grown up enough to be listened to when they say “no, don’t touch me.”