So she was 16 when F Troop went on the air? Haven’t seen the show in a long time but still, I doubt that.
Supposedly she claimed to be 18 and lied about her age a bit. It wasn’t such a big deal in 1965, and she never really did a romantic scene with the Captain, so they might have known.
Mila Kunis, for one, fibbed about her age far more recently.
Underage actresses have always been in demand in Hollywood.