As of April 16, 1862, the Confederate government required military service of all able-bodied white males between the ages of 18 and 35. By early 1864 the upper limit had risen to age 45. On Feb. 17, 1864, the government created two classes of reserves, junior reserves for those of age 17, and senior reserves for those age 45 to 50.
You won't believe this, but to keep out of service or get in a 'safer' military unit, some men actually lied about their real age! It's not uncommon to find men who seem to be a couple of years short of 45 in the reserves, and some in their late 40s who managed to stay out of the reserves.
Those remaining after these calls could be enrolled in state service. Keep in mind that many state organizations included men who eventually became liable for Confederate service. That means there could be two or more service files for the same man.
Also keep in mind that state service was for limited periods of time -- thirty days, ninety days, at most six months. When the term of service for one unit expired, a man might enroll in another. I recently copied service files for a South Carolina man who served in at least three different state units.
Last point, and this may totally muddy the waters -- by the summer of 1862, large parts of Mississippi were not under Confederate control. For that reason the Confederate government acknowledged that the Conscript Act of April 16, 1862, and its many subsequent ammendments could not be enforced in many Mississippi counties. The state was allowed to recruit in these areas as if the Conscript Act had been suspended. Some state commands raised in this manner were eventually turned over to Confederate control.
State and Confederate military laws are a lot like state and Federal tax codes. Depending on who you are, certain conditions are supposed to apply. However, the tax code changes every year, and once you dig into it, almost anything is possible!