Bearing balls can last a very long time. I have a pair of wheels that were on my 1973 Raleigh Professional. The bearings have never been replaced and I rode that bike for over 27 years only doing regular maintenance. The axles still turn as smoothly as when the wheels were new. The bottom bracket from that bike is now on another bike still as smooth as it was in 1973 with nothing having been replaced other than the grease.