[relee]

Really, 16!

I know some very smart 4 year olds ...

and my cat is a lot smarter than many 16 year olds.

[pepsionice]

I would be willing to go down to 13 years old, but you’d have to pass a civics test prior to that, and pass a 100-question test. That might disqualify most folks for the rest of their life.