You could take it a lot of ways. A retired E-5 (Army Sergeant???) would likely have the means to procure civilian leather. If you want a literary reference, the book Cowboys in Uniform, talks exclusively about the Rough Riders. But, they were all volunteers. Not someone to retire from. As a grunt, assuming you mean infantry, that would not be for you. So, you need to make some decisions. Authentic or not, More civilian or military? ect....
Now, I think that a lot of military guys may be like me, I am a Reservist, and I find myself having a hard time putting on a uniform to shoot CAS, so your character may want to do away with the uniform, especially a retiree....food for though.