As a test case you can see whether younger "grunt-level" workers tend to be friendlier than the older ones since they can't actually get higher level jobs just

As a test case you can see whether younger "grunt-level" workers tend to be friendlier than the older ones since they can't actually get higher level jobs just yet so they make the most of what they can with what they have. But in a few years these youngsters may have moved on to better jobs due to their friendliness. On the other hand, younger people may just be less bitter since they haven't been working as long at "grunt-level" as the others.