My other half is quite traditional (protestant) and was very eager to get our daughter Christened as young as possible. Our lovely CofE vicar was quite surprised and said that that's quite unusual these days, they were able to fit her in at 3 months but only by having a separate service rather than during the Sunday Mass with all our Church friends there as we would have preferred. By the time our Son came along, however, we had developed into the sleep deprived parents we are now and weren't quite so worried about the timing! We waited until about 9 months old in order for him to be welcomed into our Church in the main Sunday Mass, surrounded by our lovely Church Family, which was the most important thing for us.