No. It does not matter if the person to whom the actor is chatting is underage. 33.021 (1) states:
(1) “Minor” means:
(A) an individual who represents himself or herself to be younger than 17 years of age; or
(B) an individual whom the actor believes to be younger than 17 years of age.
Texas Penal Code Sec. 33.021:
(d) It is not a defense to prosecution under [TPC 33.021] Subsection (c) that:
(1) the meeting did not occur;
(2) the actor did not intend for the meeting to occur; or
(3) the actor was engaged in a fantasy at the time of commission of the offense.
(e) It is a defense to prosecution under this section that at the time conduct described by Subsection (b) or (c) was committed:
(1) the actor was married to the minor; or
(2) the actor was not more than three years older than the minor and the minor consented to the conduct.