Kelly's thoughts on Christian maturity: Jesus said we'll know them by their fruit. Look at what their life is producing. The problem is we are all sinners, saved by grace. So we'll all have some rotten fruit from time to time. The question is are we characterized by fresh fruit with an occasional rotten piece; or by rotten fruit with only the occasional fresh piece?
I think just as we are all unique and have different gifts (and sins) we all would have a different "first sign" of maturity. For me, I think it was seeing others through Jesus eyes in a non-judgmental way.

I agree with Kelly but if you've tripped by here before you know I have some other ideas to toss into the discussion. Kelly got me thinking about our fruit. In Galatians Apostle Paul tells us our fruit will exhibit these qualities that mark maturity as a Christian. May we all do a fruit check on ourselves: These are the traits of mature saints:
love * joy * peace * patience *kindness * goodness * faithfulness * gentleness * self-control
Immature fruit in nature is utterly unusable; so a Christian is limited in use until these maturity traits are operational. As I look over this list it seems I am developing these attributes in the order that St. Paul has listed them in Galatians. As Kelly mentioned, unconditional love filled my heart as soon as I was saved from my sins. In fact, on eating and a few other things I'm still pursuing "self-control."
One caution: our human nature draws us to become "fruit inspectors" of others. I find it's a fulltime job to inspect and maintain my own "fruit."
What do you say on "fruit" of saints?