The young man is likely less aware of the ways of the world, and more accustomed to following directions without fully comprehending the import or the consequences. To the young man, time is infinite, and spending it directionless without purpose is of little regret or concern. The not so young man is less generous with his most valuable depleting resource. The not so young man knows the absurdity, inequity, and unkind face of war. The young man speaks in platitudes, and has a clear dictum on the purpose of his service.
The young man lacks wisdom and insight to put inconveniences and suffering in perspective. He lacks the capacity to compartmentalize properly the intellect and the emotion. He can become weary with personal investment in things outside of his control. But still, a young man can be more content to waste his time, is less aware that he is wasting it, and is more steadfast in the clarity of his work.