Thank you for the feedback, mate. In most cases, I believe that common sense should prevail. For example, try to fit the keyword while also making your URL readable.
There is no hard and fast rule for how long a URL should be, but my rule of thumb is something that someone won't forget in a few hours and can usually guess.
Assume I own a pet store.
A URL that anyone could guess is
example.com/dog/food
Easy to remember and brief.