How long do coil on plugs usually last

Just too many variables to give a suitable answer. I've had some crap out way too early due to harsh environment and others last 140K miles and still going. You can test your COPs, there are simple tests you can do with a basic multimeter, or more specific tests you can run with a KV and ARC tester.

I went more than 100k on my Ford coils.

Getting them wet is the fastest way to make them fail. Don't wash your engine!

Usually they will last 100,000 plus miles. As Ken posted above some may cause problems at much earlier mileages. Coils are difficult to properly test and may test good and cause issues. The interface at the spark plug can cause issues also.