It not established in the study (that I can see in their findings) that people under 50 were wearing mask less than those above 50. The finding only showed that

It not established in the study (that I can see in their findings) that people under 50 were wearing mask less than those above 50. The finding only showed that those under 50 did not benefit. There could be any number of reason why the result of the data look like it is. If those villages are mostly small farming communities it might be that young people spend most of their time outside on the fields or herding animals while the older population spend more time inside. It might be that the older generations after a long hard working life need more active help from younger family members and can't do distancing (like in our elder care facilities). Mask has a rather good track record when people are working inside in close physical proximity to risk groups. Since the study did not explore those question we can only speculate.