Many sewer pipes are made from cast iron, so they have a lifespan of maybe 30-40 years at best. Once they reach that threshold, it is possible that they could fail at any time. Tree roots, cracks, and other issues can further that damage pretty quickly.
The main thing to look at is sewage backups. This indicates a blockage. If you see it every time you open a drain or flush the toilet, then there’s a problem.
Damaged sewer pipes also tend to smell pretty foul. You’ll have the odor in your home or business.
I’d also look for patches of your lawn that look better than other spots. Sewage leaks often act like a fertilizer, so the places where a leak would be will appear thicker, greener, or both.