Tex. Est. Code § 251.107
Notwithstanding any other provision of this subchapter, a will written wholly in the testator's handwriting may be made self-proved at any time during the testator's lifetime by the attachment or annexation to the will of an affidavit by the testator to the effect that:
(2) the testator was 18 years of age or older at the time the will was executed or, if the testator was younger than 18 years of age, that the testator:
Added by Acts 2009, 81st Leg., R.S., Ch. 680 (H.B. 2502), Sec. 1, eff. January 1, 2014.
Acts 2017, 85th Leg., R.S., Ch. 844 (H.B. 2271), Sec. 18, eff. September 1, 2017.