Someone recently called me a "baby Christian" after hearing I was just baptized in 2006. I know the term is sometimes used to describe new Christians or those who are "stuck" in their walk early on. The term ruffles my feathers especially when referring to a new Christians.
My issues is that it sets up a superior/inferior relationship amongst people. "You are a baby, I am the adult" so therefore more mature than the person being called the "baby". Am I a new(er) believer? Yes. Do I have a long way to go to becoming more Christ like? Absolutely. Does that make me a baby? No.
It doesn't matter if you are a new believer or grew up in the church, if we are still on earth we have a long way to go in our walk. Life is a continuous learning process for everyone. I have just as much to learn from someone who has been a Christian for 60 years as I do someone who has been one for 60 minutes. Every person brings their unique perspective and personality into their Christian life. Look at Paul -- he was a new believer but he was no "baby" in his walk with Christ.
Instead of attempting to label someone, how about next time you try listening and learning something from them instead? You might just be amazed at what they have to say.