Linda Hayden just 16 years old in this film
If you look at the titles at the start of the film, shown in Roman Numerals it was made in 1969, but released in 1970, which made Linda barely 16 years old.
I'm not sure if she was supposed to be 16 or a little older, but if she was supposed to be 16, you could perhaps understand her father's wish for her not to flirt with an older man.
Even though the father was a hypocrite.