>>>I think 25's about when personalities stabilize.
I was married before 25. I don't think a personality stops stabilizing. You never stop experiencing new things. You adjust as you go.
So you wouldn't want MIL enlisting until 25?
That was my experience as an early adult. I'd only date wimmin over 25, something happens about that age, and they were significantly and very noticeably more mature.
Of course, my other take on the matter is that anyone who's liable for taxes should have the vote... which means everyone.
I'd go you one better. No Taxes. No Vote.