I may have down my math wrong, but I subtracted minors. Though there’s a case that 16-18 year olds should vote.

There would still be plenty of non-voting children. And with 16-18 year olds, the case is there but it’s a case of being careful what you wish for. You open up a pandoras box of a bunch of willingly-uninformed voters (because most kids don’t care about politics), along with a bunch of teenagers who aren’t concerned about the consequences of their actions and would gladly vote for a shitty candidate “for the lulz”. Personally, I see it as a case where you’d be flooding the polls with so many uninformed voters and intentional trolls that the results would essentially be up to random chance. But I do agree that there’s a case to be made, even if I think it’s a terrible idea.

Felons should be voting if they’re adult citizens.

In principle, I agree with you. I’m just saying that this is stated in the Constitution and we cannot just ignore the parts of the Constitution we don’t like.

Is there an intelligence requirement for voting?

No. If Jim the meth-head and his sister/wife want to head down to the polls, they should absolutely have the right to do so. But I was talking about people who do not have the mental capacity to vote. People with severe Down Syndrome, for example. Non-verbal people with special needs. Dementia patients. Those with mental health disorders who think that the people of Jupiter are trying to read their thoughts by using laser beams disguised as rainbows.

I would also include elderly people in nursing homes, hospitalized people, and people who are otherwise unable to exercise their right to vote because of forces outside of their control. They should have the right to vote but are often prevented from doing so, even if only because of simple things like staff members being unwilling to bring them to the polls.