The Confederate Conscription Law, when first enacted on April 16, 1862, required three years of military service of all white males between the ages of 18 and 35 who were not legally exempt from service. As the war dragged on, and the pool of recruits became smaller, the Confederate Congress modified the upper limit to 45, and then to 50. However, men who were older than the specified age could voluntarily enlist; it's just that they were not obligated to do so.

So it was not unusual for men over the age of 40 to serve in the Confederate army. Incidentally, the lower age limit was reduced to 17, but boys younger than that frequently enlisted, especially toward the end of the war.