I think this is a bad habit older people get into with younger people, particularly teenagers.
The "Oh, haven't you grown!" statement. I hear it all the time from relatives with both of my stepkids and one is male and one female. It should stop by the time you hit 21 hopefully. It's just one of those annoying "adult relative" things you have to live with I'm afraid.
My stepdaughter is 5'11" by the way and I have said this to her on many occasions and she enjoys being tall. It is a good thing whether male or female. My ex bosses daughter is 6'2" and she still gets these comments at 25 years old.
With you being only 18, it's ok these days, as youths are getting taller and taller regardless of gender so you should be ok to grow even more yet lass

Like Shang has said, most people think tall is sexy, so embrace it.
John