To add to the responses, Yes, all men of eligible age registered for the draft in World War I. When the draft began, all males aged 21 to 30 were required to register. Then in August 1918 Congress expanded the age range to include all men 18 to 45. Your library probably has a subscription to Ancestry.com if that helps. Alternately, if you ask the forum to look up your grandfather's registration for you, someone can do that, but would need his name. If you can add the place where he lived, his spouse or parents, that would help the forum find him in the draft rolls. If he was born as late as 1903, he was too young. Hope this helps.