what is the life span of avent storage cups? how often should i discard & change?

It is BPA free. http://www.mea.philips.com/c-p/SCF720_10/avent-avent-food-storage-cups I did not use it to store breastmilk. I used them to store puree food when kids were young. I think as long as the cups do not turn colour or damage, you can continue to use it.