The 6th (also called the 2nd and Stone's) Regiment Texas Cavalry was organizaed in September, 1861 for 12 months. It was re-organized under the Conscript Act in May, 1862.
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D. B. Thomas, age 33, enrolled as Surgeon, 2nd/6th Regiment Texas Cavalry, August 15, 1861 at Dallas, Texas by B. W. Stone for a period of 12 months, dropped from rolls about September 8, 1863,
M323: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Texas
I believe the pre-war militia was a great social organization for young dandies to belong to.