I grew a few inches after I turned 18, and I think it was caused by taking multivitamins and eating less junk food and more fresh fruits/vegetables. (I also started doing yoga around that time, so I can't rule out the possibility that it played a role in growing, too.) I grew a bit more after I was 21, and I think it was from stopping being a vegetarian and adding a vitamin D supplement (which probably indirectly helped with my calcium deficiency, hence the height increase). If you're not on T and are planning to start, doing so sooner would be more likely to increase your height than if you wait.