A large proportion of the officers and men in all the reserve regiments and battalions were exempts from the regular Confederate service, many of them having been honorably discharged on account of wounds or failing health; many others were employes in government workshops, and some were State and county officer, while still others were either too old or too young for the regular service.
I realize that you're simply quoting from the CMH volume VI on Georgia, but this statement is wrong on almost every point. If the part about those discharged from service was true, we could easily find names of soldiers who had prior Confederate service on the rolls of Georgia Reserves units. The law of Feb. 17, 1864, was intended to replace able-bodied men employed in government workshops and arsenals, not to enroll them in the reserves. Also, state and county officers were still exempt from Confederate as well as state militia service. Furthermore, since teens and older men who became subject to service as a result of the law were required to enroll, it's a bit misleading for the author to state that reserves were "either too old or too young for the regular service."
The military law of February 17, 1864, and its impact on bringing new men into the Confederate army provides an interesting topic for review and study. Here's a recent article about that subject as it concerns the State of Georgia --
http://muse.jhu.edu/login?uri=/journals/civil_war_history/v050/50.1morgan.html