Heck, why have an age requirement at all?

Maybe we should change our voting eligibility requirements to reflect a demonstration of actual maturity, e.g. attending school and/or gainfully employed, paying more in taxes than receiving in direct government welfare payments, owning outright or up to date on loan payments for real property, raising children in an intact biological or adoptive family and/or having raised children who meet the other criteria.

Could this cause a problem with miscreants gaming the system? Yes, but it would solve multiple problems too.