19.5 are commercial size and those usually have 10 years life span.
My experience with multi-layer commercial tires is that even big cracks on the outside layer still leaves you several layers of reinforced rubber under.
Would you start seeing fabric, that is another story.
You can do 2 things IMHO.
1 check the tire manufacturer site for recommendations and even email them pictures with question
2 go to commercial tire shop for inspection. Don't talk to yesterday's burger flippers who change tires today at "American Tire" or "Costco"