buy something right around your height/an inch or two taller. If you're like me and ride your skis for a while (3/4 seasons) you will be pretty much as tall as you are going to get when you are 18/19. So if you have a huge growth spurt (say 6 inches) then your old skis will still be useable (around chin height) just kind of short.
I bought some 171 chronics back in 2016 when I was like 5' 9"-5' 10". I grew to 6' 2" and they were around chin height. I then bought longer skis.
Also keep in mind you will find the best deals on skis in the summer time, so unless you need a new pair right now, I would wait.