Ropes: How old is too old?

I just got back into climbing after a 6 year hiatus while living in Austin.  Though I had fairly new ropes that were well maintained before I moved, I wasn't sure if sitting for 6 years (in a rope bag) in 900 % humidity was ok to climb on.  My thought was, "there is only one way to find out" and I wasn't willing to risk it.  Sadly, I ditched both ropes. 

Recently a friend was going through something similar and this lead to our question:  Is there a way to test you ropes?  What is your baseline for rope replacement?   Thanks!