I stopped growing about 7th or 8th grade, but I did actually gain a few inches after starting T. I was 5' or 5'1" for the entirety of high school, I started T right after I turned 18, and now at over a year on T, I am in between 5'3" and 5'4"
It varies greatly by person, but it is possible that you can grow into your twenties. It does not mean you will, but it is possible.