How long do bibs/shorts last?

I’m riding on average three times (maybe 5 hours) per week, and I’ve ridden just over 3,000 km since I started cycling one year ago, so I don’t expect to need new shorts for a while yet… but I want to know what I should be looking for to see when I do need to change my shorts, especially since I’m substantially overweight and figure that may make a difference.

Thanks for the comments, I appreciate the input.