More than a million adults have legal guardians. In seven states, they can't vote.

Well, that's true, but the hormones of a 15 year old impair their wisdom. Unless there is significant cognitive deterioration a 70 year old would have no problem with that.

And, I'd bet on average the 70 year old has more weslth, breadth and length of experience. Pulling it 100% out of my ass though, no data to back it up.