A refinement of my idea here. Minors should continue to have weighted votes to be exercised by their parents, but each parent should be allowed only one vote in addition to his or her own. That way, parents don’t get credit for having too many children. (Polygynous people of whichever religion will get credit for as many children as there are wives, plus 1, which sounds fair.) Now, I don’t think that it makes sense to argue that this will provide an incentive for parents to “game the system”. Those who think that it makes sense have obviously never had children themselves. But the point that it will overweight the votes of people who did not practise birth control is well-taken, hence the modification.
Second modification. The weights should be discounted. We should use the five-year average rate on government securities of appropriate tenor to determine the discounting. That will mitigate the advantage enjoyed by young people somewhat.