When is a phone old

Hello, An article stated that phones should/could be replaced when they are four years old. That seems rather limiting to me. Our phones are almost three years old so it is coming. I did check the battery and it is no longer able to get back full power or at least it is at 89% whatever that means. I suppose it is nice to upgrade, but would we use much of the additional capabilities? I often think there are hidden treasures in the phone that I cannot access, because I do not know about them or even think to check into it. I now often use voice commands to write texts and just recently decided to put the person’s name in the same way. It certainly helps if my hands are occupied or dirty. Just now I figured out how not to include the word send in the message. I suppose one advancement that I might notice with a new phone is that the camera is better than the one we have. Perhaps there is some other trick that I would discover by accident or possibly someone might tell me about something that is just what I am waiting for. In all my growing up years we only had two different phones in the house. A wooden wall phone that cranked was the first and the second was a dial phone. It certainly is a different time when the new becomes old as I turn around. Paula