Draft Fibbing?

David Roy COCHRANE was my great-grandfather (paternal grandmother's father). I had a birthday for him of 28 Sep 1889, per his WWI Draft Card. Several days ago, I ran across a listing online for him, with a birth year of 1892. I brushed that off, going, of course, with his own affidavit, as the draft card has his own signature.

Today, I was digging through Mom's files and found a slim stack of papers my Aunt had sent to her regarding Dad's side of the family. I brought them home and found several photocopied pages from an old family bible. I can only assume that the bible was a wedding gift for Edward Cochrane and Della ADAMS, as their marriage is listed on the main "Holy Matrimony" page. Their firstborn son was David Roy, and Della listed his birth date as 28 Sep 1892. Well, that's strange.

So, I began putting David's siblings into Ancestry.com. I'm searching for 1900 and 1910 Census records for the family and figured, the more names the better. David's next sibling was Oscar Orval Cochrane, b. 3 Dec 1893. What pops up for him but a WWI Draft Card, DOB 3 Dec 1890.

Hmmm....three years' difference for Orval. Three years' difference for David. And both cards claim exemption from the draft on these grounds: "wife and child." Could the brothers have conspired to make themselves three years older for the draft and therefore avoid being put into battle? It's possible, although the National Archives state that Selective Service Draft Registration at that point (5 Jun 1917) was for all men ages 21 - 31. Were men over age 25 less likely to be sent to war? Definitely something worth researching.