Tina Lawton was a yeoman third class serving in the sciences division aboard the USS Enterprise in 2266.
In that year, Lawton was introduced by Yeoman Janice Rand to Charlie Evans, a seventeen year-old boy whom the Enterprise was transporting to Earth Colony V. Rand had been made to feel uncomfortable by Charlie's affections, and introduced him to Tina in an effort to facilitate his association with a girl closer to his own age. Charlie rebuffed Tina, however, wanting to further pursue a relationship with Rand. Later, out of frustration with the Enterprise crew, Charlie utilized incredible psychokinetic abilities granted to him by the Thasians to transform Tina into an iguana. Along with all of the other crewmembers affected by Charlie, Tina was restored by the Thasians when they arrived to retrieve Charlie. (TOS: "Charlie X")
Background
Yeoman Lawton was played by Patricia McNulty. Yeoman Rand introduced her as someone Charlie's own age, and he was seventeen. However, most later Trek productions portrayed Starfleet as generally being an eighteen-plus organization (although Wesley Crusher and Peter Preston were both supposedly 15 years old when they entered fleet training). Yeoman Rand could also have been generalizing.