Diagnosing plant problems, especially from afar, can be tricky. I once consulted by phone with someone about her ailing plant that seemed to exhibit symptoms of inadequate light. When asked, she said that it was on a north facing windowsill, which should have been ideal light for her plant. It was only after exploring many other options, that she mentioned that she kept the blinds closed during the day so her carpet wouldn't fade! Bingo!
Another problem is that if light or water, for example, are a bit off, it may take several years before significant symptoms start to show.
There is no life span limit for your Croton, so old age is not the problem. I am surprised that it has really needed repotting every couple of years. Reduction in plant growth is quite common following unnecessary repotting. That is because the plant puts most of its energy into filling the pot with roots at the expense of foliage growth.
Make sure your Petra is getting enough light. Water it as needed, not based on what it has used in the past. It may be using less now than before. Otherwise, be patient and remember that as long as it is not deteriorating, it will probably resume growth in due time.