Remember that more than fifty years have passed since Beowulf returned and assumed rule of the Geats. He must have been some seventy-five + years old! Is war a young man's game? Is leadership?
Excellent point, Linda, although there are still "old" guys out there fighting and dying for us, while there are young(er) men sending them out to die.
This is a tough one, especially given current events!
Have you seen the movie Troy? When the kings gather to congratulate Agamemnon for "his" victory on the beach of Troy, Odysseus reminds Achilles that "war is young men dying and old men talking." That's an excellent description of war: old men plotting the strategy, and young men carrying it out.
I had to ponder this one long and hard, and I'm not entirely sure I have a definite opinion yet!
Initially I thought that Beowulf was a better military leader when he was younger...he was more full of life back then. But then it occurred to me that he wasn't really leading men in the stories we read about him - rather, he brought a bunch of guys from home to back him up in his efforts, but never really needed anyone's help. I think he actually spent more time talking to his men, letting them know the importance of certain things in life, when he was old and facing his final foe, the dragon. Granted, he still told them all not to worry their pretty little heads about it, he'd just do it himself, but he did have some nice parting words for them.
Now, to look at the question from a modern-day military standpoint (which I can't really do as I'm not military, but I can make a few guesses, I suppose), I would say that war is a young(er) man's game. Older men tend to be more cautious, and if it's a war that is necessary, you need the youthful energy and strength, and yes, even naivete of youth.
That having been said, I do believe leadership is appropriate and right for older people. We need their experience and what they've learned during their lives to help us make good decisions.
Of course that doesn't mean all older people are good leaders, or that all younger military men are good in war. Just a few thoughts from a tired brain!