Tex. Parks and Wildlife Code § 42.0175

(a) A license issued under this chapter, other than a lifetime resident hunting license or a nonresident five-day hunting license, is valid only during the yearly period for which the license is issued without regard to the date on which a license is acquired. Each yearly period begins on September 1 or on another date set by the commission and extends through August 31 of the next year or another date set by the commission. A license issued under this chapter other than a nonresident five-day hunting license that is issued before September 1 or another date set by the commission and does not expire until August 31 of the next year or another date set by the commission is valid from the date of issuance through August 31 of the following year or another date set by the commission. The commission by rule may set the amount of a license fee for a license issued during a transition period at an amount lower than prescribed in this chapter and provide for a license term for a transition period that is shorter or longer than a year.

(b) A license issued under Section 42.012(b) of this code to a person who is 16 years of age at the time the license is issued, but reaches the age of 17 during the term of the license, is valid for the entire term of the license.