I heard the other day it was legal to marry your first cousin in TN. I had to look up the validity of this, and low and behold here's what I found. I think it's very interesting to look at the states that allow it, but only under certain conditions.
Check this out: Kissing Cousins
It appears to me that for those states in the third column, if you are 55 or older they think you won't be trying to have a baby anytime soon.