There is no John Turner among the men of K/5 TEX in the Compiled Service Records. The men surnamed Turner in this comapny in CSR appear to be CAPT Ike N. M. Turner; 3 LT Joseph Turner; and Privates C. H. Turner and W. H. Turner. However, the muster rolls of this company are fragmentary, and it is quite possible he enlisted and served during a period for which the muster rolls are now misisng. He is not listed on the Appomattox paroles.

Given the age you stated, it is likely he enlsited reasonabley late in the war. There were always exceptions, but most Mothers and Fathers were reluctant to let their children enlist until they reached conscript age, which was 18 when first set in March 1862, and lowered to 17 by 1864. If his tombstone was issued by the Veterans Adminsitration, there was a loose form of verification of service. If it does not specifically mention Hood's Brigade, there is the chance that he served in another Texas unit, such as the 5th Texas Militia, 5th Texas Cavalry, etc. Tombstones have scads of erroneous or partial information about the unit of service.

If you are close enough, I would suggest you start at the Confederate Research Center at Hill College, Hillsboro, Texas. In addition to the muster rolls, the Research Cneter has the reunion records of the Hood's Texas Brigade Survivor's Association, which met annuallly from about 1870 until 1931, and he may show up in those. You should also check to see if he or his widow drew a Confederate pension through Texas; if so, the pension records at Austin could help a lot. There is a published index to Texas Confederate pensions.