phillips such nonsense....
im 20 (as of yesterday) and i carry full modern combat kit along with my ruck all the time which in total likely weighs much more than plate armor did. as well armor harness' then were impressive pieces of physics as they distributed weight shockingly well. knights were not the turtles people like to say they were and there are accounts of fully plated knights jumping into their destriers saddles.
as well as a twenty year old i weigh 195 pounds at 6'1'' and can bench 200+ pounds, squat 375 pounds deadlift 300 pounds and hang clean 185 pounds multiple times. so yeah a boy my age is more than capable of having the strength and endurance of a older man. in all honesty i was even bigger in high school when i was 16-17 from football though i had far less endurance. when i was fourteen entering high school i weighed in at 170 pounds and was already 6' and my parents did not allow me to lift weights until i did high school sports.
and then there are 17-18 year olds in western armed forces who are physical specimens and run around the modern battle field in full kit and fight.
the fact you think that men cannot fight until 21 years of age is absurd.
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