Neither Texas nor any other state has a law so intrusive as to govern the ages at which two persons may date each other or hold each other's hands. The extent to which "kissing" is legal depends on what body parts are involved, but there is no law that regulates lip-to-lip kissing.
Your statement that the "age of consent is 17 in the state of Texas" is incorrect.
Section 21.11(a) of the Texas Penal Code provides that it is a crime to engage in "sexual contact" with a person under the age of 17, unless the older person is "not more than three years older than the [younger person] and of the opposite sex."

