Bushings made of rubber would be designed to last about as long as rubber hoses, generally the lifespan expected would be about 15 years, which for most would be the life of the car. The environment they are in will affect the lifespan.

How many miles will a bushings last?

The lifespan of a control arm bushing varies drastically depending on the type of vehicle, manufacturer, and driving conditions. From what I've gathered, control arm bushings can last between 40 and 100 thousand miles, with an expected lifespan of 80,000 miles.

How often do you need to change bushings?

You want to at least do a good inspection/adjustment every 50hrs of riding. If you ride 1hr every week, that means once a year.