Hello, in general I would say that it should not be older than two years. Provided, of course, it is in the tube and sealed. I recently threw away half a tube, and it was three years old. It took a lot of effort to get it out of the tube.
Hello, so purely from the durability I would say almost every year or every two years.
I've been using the paste for a few months now and can only report good things about it, except that I think it should be changed more often.