This is often interpreted as applying to soldiers: one they are (allowed to be) married, they are no longer sent on dangerous missions. As with the previous line about the empress, however, this would seem to narrow the application to a small slice of people. I think the point with the women in the previous passage and the men in this, is that they have reached a point in their lives when they must take care of their health. It is no longer worth wearing themselves out for either physical appearance or professional advancement. And if people are smart enough to take care of their physical health, how much more so their spiritual!