@g-flex
Way to jump to conclusions, bucko!
I'm not arguing everyone has the same aptitude at everything. MY issue is the arbitrarily basing all these laws on age instead of said aptitude. Do any of the things you listed have anything to do with the number of revolutions someone has done around the sun? No, they have everything do with mental, social, and physical development instead. Not only that, everyone grows and develops at different rates. There are 12 year olds more mentally mature than you or I, out there. What's another word for making assumptions about people based on arbitrary shit? Oh yeah, prejudice.
And when I mentioned practicality, I meant it for things like voting rights and consent. How exactly would you test capacity for those? Gonna give out a politics test before people can vote? As such, I'll concede age limits on those sort of things only because actually being fair and moral is almost impossible to accomplish.
My beef, ultimately, is the idea that people can somehow be inherently inferior. You can be inferior at a task. You can be inferior at knowledge of a subject. You can't be inferior as a human being. If we give rights to human beings, you need damn good, provable, and practical reasons to take them away from any particular individual, not the group they belong to. Blanket, arbitrary removal of rights is never a moral action.
So in other words, if your argument is "most kids can't do x action, thus shouldn't have y right" my reply would be "base the law around being able to do x action to have y right, not age."