You don't have to be in the military to wear military wear. Military wear used to be found only in Army/Navy Surplus stores, which are good places to go to find a bargain if there are still stores like that in your area. If you decide to go on a second-hand hunt look for leather bomber jackets or a nice pair of lace-up black army boots.
Don't despair if you cannot find a used clothing store in your area that specializes in Army/Navy surplus, because the designers have caught the trend and they are offering many military wear styled items as part of a current fashion trend. There is something to be said about a man in uniform and the influence of military wear on fashion has been consistent for many decades.
It is interesting to note that you can wear military wear as a rebellion against the military as well as to show your proud patriotism. In modern times, this can go either way so few will see it out of place. U.S. flag emblems can be sewn on virtually any type of clothes to add that patriotic feeling, although we have yet to see them sewn on tuxedos. Maybe that is pushing it a bit too far.
The main military wear we see, or at least the iconic symbols of it, are in the boots and the jackets. The idea is not to look like you are in uniform, but that you create a nice look with the accessories being military denominated in their style. Lace-up black boots, also called jack-boots are just as acceptable for casual fashion wear as they are to put on when you plan that day to parachute out of a plane.
You probably want to stay clear of camo-wear, short for camouflage wear, which is the shirts, jackets, and pants that are patterned with dark greens, dark browns and black for the jungles of Asian countries where we fought wars decades ago or the more modern tans and dark browns meant for soldiers' use in desert climes. Camo-wear is designed to supposedly let the soldiers blend in with the local scenery. You can wear a single piece of camo-wear and pull it off quite nicely, but you would not want to have your entire outfit made out of it.
Unless you are actually in the military, that just looks like a clown suit. As we said, military boots are AOK and most importantly the height of military wear fashion is a military style jacket. Some of the major designers offer these in retro- looks that hark back to the times of WWI and WWII.
These are the very popular leather bomber jackets which have never seemed to go out of style. Also popular are the full length dark navy blue wool jackets. They are called "navy" blue because that was the color chosen by the U.S. Navy. They also always look good. If you cannot find a second hand one in the Army/Navy Surplus store for less than a hundred bucks and have tailored for another $50 you may have to pop for the designer copies that will run you 5 to 10 times that price.