Reading Sir John Smythe and Harold Lamb and Martin van Creveld, I was struck by the fact that sometime in the 19th or 20th century, armies began to fetishize youth. A friend joined the Canadian Army Reserve at 17 and was carrying a rifle in Kandahar a year or two later, and when Martin van Creveld wants to show how Prussian supply officers were inadequate in 1848, he accuses them of being aged from 55 to 69 (Supplying War p. 78). My colleague Jolene McLeod has listed the modern authors who insist that Plutarch cannot be correct that Eumenes’ Silver Shields were all 60 years and older when they marched up to Antigonus’ phalanx and stabbed it to pieces in a few moments of blood and horror (Life of Eumenes 16.4). An American speaker calling for a reform of the relationship between their regular army and National Guard wanted the former to be “young” and focus on warfighting, while the older National Guard soldiers could focus on rebuilding and garrison duty. (It might have been this TED talk by Thomas Barnett but I don’t have energy to re-watch it).
So at last the Great War blazedAl Stewart, “Old Admirals” https://alstewart.com/old-admirals
I waited with the passing days
The call to arms that never came
I may be old now in your eyes
But all my years have made me wise
You don’t see where the danger lies
Oh call me back, call me back…
And yet when I ask soldiers who died before the year 1800, they have a completely different attitude. Sir John Smythe says that all ancient and modern nations agree that soldiers should be at least 18 years old, but he thinks that might be too young: “of the age of. 18. I would haue none elected vnlesse they were of so great growth, & corporall disposition, as that they were able to perform the duties & effects of souldiors, which verie fewe at that age can.”  Polybius’ Romans and Thucydides’ Athenians relegated eighteen-year-old soldiers to easy duty such as skirmishing and guarding fortifications. And Timur destroyed Sultan Bayezid’s army in 1402 at the age of 66 and was on his way to invade China when he died three years later. When soldiers before the 19th century speak to me, they don’t think teenagers are ready for serious combat, and they don’t think generals get mouldy when they turn 50. They think that as a rule of thumb men should not have to fight after an age between 45 and 60, but they are not absolute and do not think that is too old for a general.
Johann Schiltberger has a terrible story of what happened after the crusaders were defeated at Nicopolis. Sultan Bayezid discovered that before the battle, the crusaders had killed all their prisoners:
So they came the next day, each with as many prisoners as he had made, bound with a cord. I was one of three bound with the same cord, and was taken by him who had captured us. When the prisoners were brought before the king (Bayezid), he took the Duke of Burgony that he might see his vengeance because of his people that had been killed. When the Duke of Burgony saw his anger, he asked him to spare the lives of several he would name; this was granted by the king. Then he selected twelve lords, his own countrymen, also Stephen Synüher and the lord Hannsen of Bodem. Then each was ordered to kill his own prisoners, and for those who did not wish to do so the king appointed others in their place. Then they took my companions and cut off their heads, and when it came to my turn, the king’s son saw me and ordered that I should be left alive, and I was taken to the other boys, because none under XX years of age were killed, and I was scarcely sixteen years old.J. BUCHAN TELFER (tr.), THE BONDAGE AND TRAVELS OF JOHANN SCHILTBERGER (London 1879), p. 4 https://www.gutenberg.org/files/52569/52569-h/52569-h.htm#Page_4
Killing prisoners is a terrible and wicked act. But Bayezid’s understanding of a ‘man of military age’ was more restrictive than the one US forces use when they justify the results of the latest bombardment or drone attack! The CIA World Facebook used to consider any male from 15 to 49 as a potential soldier, and since 2001 I have seen government statements which reckon any male 16 and older or 18 and older as a possible combatant whose death does not need much justification.
I am not a soldier, and I have not even had a chance to play the group-combat games I would like to try. I don’t want to say that the moderns are wrong in a modern context. But I am confident that their cult of youth is wrong for contexts before the 18th century. I trust the professional judgement of soldiers who lived and fought in that context over the judgement of people who never put on an iron cuirass or saw an arrow shot in anger. And I wish I understood why modern ideas are so different from the ideas of the ancients. I am interested to hear from Hollie McKay that during the wars in Syria and Iraq in the 2010s, she saw men in their 60s and 70s fighting with the peshmerga (War Scholar podcast 13 April 2021 # 33:00 http://warscholar.org/why-the-battlefields-of-isis-were-so-horrible-with-hollie-mckay/).
I have talked about this before as In Antiquity, Fighting Wasn’t A Young Man’s Game (2019). Journalist Thomas E. Ricks says that George C. Marshall prepared for US entry into WW II by retiring a crowd of older colonels and generals (warning: YouTube).
(scheduled 4 June 2021, photo added 20 August)
concerning conueniencie of yeares, I thinke none meete to be elected and inrolled vnder the age of. 18. yeares; which is the lowest age that hath beene allowable amongst all warlike nations of auntient and moderne times; nor none aboue the age of. 35. or. 40. at the most: And of the age of. 18. I would haue none elected vnlesse they were of so great growth, & corporall disposition, as that they were able to perform the duties & effects of souldiors, which verie fewe at that age can. And such as should be elected after the age of 18. I would haue to continue soldiors vntill they come to the age of 45. incase their health and corporall disposition of bodie, doo continue in them vntil that age.
And so likwise, I would that such as were elected through their good disposition of bodies to bee souldiors at 35. or 40. yeares old, should with good account and credit in the shiers where they dwell, be dismissed from being souldiors at the age of 45. and no waies further to bee emploied in matters militarie, vnlesse their wisedome and sufficiencie were such, as they were to serue as officers of bandes.