It is natural for growth to change us over time. No one thinks that seeing a grown man act like a young child is healthy. No one wants to have a mature woman need to be cared for like a immature little girl. God designed us to grow and to mature and to change over time.
Not all change is easy and not all change is healthy and not all change is desirable. But we all will change as we go through life. Children change fast. Adults change slowly. But the minute we stop changing at all something is wrong. New converts change dramatically, elder saints change incrementally.
The challenge is not just how to stay saved for the first 6 months or even the first 3 years. The challenge is how to stay saved when decades have passed and life has been lived. The challenge for our church is how to keep elder saints interested and involved and engaged without brow beating them about things that they can no longer do.
It is not a failure to grow up and mature. It is how life is lived with all of us. It is immature to criticize elders for not acting like children. It is insensitive to belittle folks who have stood the test of time and who just need a little encouragement to help them stay saved for another day.
It is unfortunate that the New Testament ends so soon and only covers the first few years of the emergence of Christianity as a stand alone religion. But maybe God knew that times would change and rather than force us to live like our ancient ancestors He gave us liberty to work things out in our time in a way that works for us. We often have to study church history in the modern world to find out how to do this.
I am grateful that I am where I am in life and that I have found a place to live for a long time. Please do not make life any harder by trying to force me to live a life that I lived a long time ago and that does not work for me any more. God is eternal, but I am not. God never changes but I change a lot.