Based on the man's age and the reference to Texas militia, it probably means William J Gilmore never joined the Confederate army. The 19th Brigade of Texas State Militia organized in 1861 with regiments from the counties of Freestone, Limestone, Ellis and Navarro. Please understand that a man did not enlist in a militia command. Rather, a man belonged simply by being a citizen within the age range set by law for militia service. For example, in 1861 a thirty-year old man living in Freestone County TX automatically belonged to one of the companies of the 1st Regiment, 19th Brigade, Texas State Militia. He could only leave this command by one of four ways --
1) A discharge or waiver of service from an authorized Texas civil or militia officer,
2) Death
3) Moving to another county or state,
4) Joining the Confederate army or navy.
When the Confederate government enacted the Conscription Act on Apr 16, 1862, most of the men in Texas militia units had to join a Confederate military command. Units like the 19th Brigade Texas State Militia went out of existence. The Texas State Legislature responded by passing new militia laws, creating new militia organizations for Texas citizens not in Confederate service.
Here are references to the 19th Brigade Texas State Militia of 1861 --
http://archive.org/details/generalordersno300texa