If you did end up as an average soldier in the armed forces, you would be 25 years old, 5 feet, 7½ inches tall, and a compact 144 pounds, with a 31-inch waist and 14-inch neck. Most likely, you would be among the 4 million American men who served in the American Expeditionary Forces. If so, you had a 50/50 chance of serving overseas, a 5 percent chance of being wounded in battle, and a 1.3 percent chance of being killed in the fighting. But, as a typical G.I. (a term that wouldn’t be in use until the next world war), you would not be among the 43,000 servicemen who died of influenza during and after the war.

Looks like the average height of an American male has since grown by 2.5 - 3 inches, or about 3.5% - 4%. Interesting little historical tidbit.