Ethics Continued

I just read that the state of Illinois is debating changing the requirements for organ donation to preference younger age of reciepient. That would mean that if I were 50 years old and on the waiting list for 5 years, but a 10 year old just came on the list, they would get the kidney/lungs/ heart/whatever before I would.
While I understand the reasoning behind this proposed change it brings up some ethical dilemmas for me. How do we value one life over another. It might seem more clear cut if you are talking an 85 year old versus a 5 year old, but what if you are talking a 45 year old versus a 35 year old? Do we add caveats for married or parent over single or no children? Who's life is worth saving more than someone elses and how do we make that decision? What are the criteria? Where does it stop?
From a Christian standpoint do we try to figure out who God prefers we keep alive? For that matter, is transplanting organs ethical from a Christian standpoint at all? Are we trying to play God, making decisions about when a person should die or when they shouldn't? Or do we assume that we have these capabilities because God ordains that we do?
I don't know what the answers are, but I am troubled with the thought of having to tell someone that even though they have been on the list the longest, they aren't going to get the organ because of some alternative criteria, beyond the fact that they are a human person in need.