I had a friend that was using a mat that was so worn from use - I have no idea how she could cut anything decently with a rotary cutter on it. The top layer was missing in places - looked like a potholed road!
If a mat is used a lot - especially if the cuts are usually in the same spots - it will wear out. Age and amount of use do not always go together. It can be six months old and hacked up if used a lot.