I've got a 17yo son and a 15yo son. Neither of them are "brainless", in fact I think they may be smarter than me.
Look at the general population. There's 40yo's out there that you wouldn't trust to mop a floor. Old folks who don't know what century it is. People with ideas so weird you don't know how they manage to feed themselves. But all these people get to vote.
I don't have a problem lowering the voting age, but it's not on the agenda here, as far as I know.