Here's why 16 is below the age of consent in Tx.
http://www.crimevictimsinstitute.org/documents/Adolescent_Behavior_3.1.11.pdf
"Although “statutory rape” is rarely used in the language of the laws, the term is typically recognized as encompassing the intent of several other named laws such as sexual assault, sexual assault of a minor, rape of a child, corruption of a minor, carnal knowledge of a minor, unlawful carnal knowledge, sexual misconduct, or child molestation, to name a few. The predominant rationale of statutory rape laws is to protect minors who are said to be incapable of consenting to sexual intercourse or other sexual activities, due to their lack of experiences to make mature, informed decisions.4 It is believed that youth below the age of consent are less likely to understand and consider the potential consequences of sexual activities, such as sexually transmitted diseases, and pregnancies. These minors are also argued to be unequal to adults, socially, economically, and legally. Because of this, statutory rape laws have been introduced to reduce the power adults may have over minors. These laws do consider that minors will consent to sex. It is the basis for the laws that even if minors consent, adults cannot engage in sexual activities with them because of the power they have over minors. What the laws do not consider is that minors are consenting to have sex with other minors or slightly older peers who do not have power over them.
The wording of these laws encompass teenage relationships making it equally illegal for, say a 17 year old to be sexually intimate with a 16 year old boyfriend or girlfriend. However, because the laws were not originally written to prosecute such cases, the law was rarely enforced among teen couples. In 1995, however, a study was published that caused many states to toughen their statutory rape laws, widening the net to include more teen romances. Landry and Forrest (1995)5, found that half the teenage pregnancies of girls aged 15-17 were the result of teenagers having sexual relationships with men who were 20 years of age or older. "
Just a snippet, lots more explanation in the link.