If you take good care of a carpet, in most cases, it should last about ten years. But no matter what material your carpet is made of, be it wool or nylon, eventually, you will need to replace it. When it is time to replace your carpet, you'll be able to tell just by looking at it.
An old carpet is a tripping hazard, an eyesore, and an allergy-causing problem. That's why if you see the following visible signs, then you should seriously consider installing a new carpet.