An earlier poster was incorrect. There was an exemption for age. The following is copied directly from the Texas State Historical Association website in the section regarding elections laws:
"The suffrage laws of Texas apply to primaries as well as to general elections and have changed over the years. Formerly all persons twenty-one years of age or above were generally qualified to vote in Texas if they met residence requirements, paid a poll tax if they were under sixty years old (adopted in 1902), and were free from certain disqualifications relating to mental condition, pauperism, conviction of crime, and connection with the armed services."