I remember thinking the same thing in my early 20s that this was it, I was the size I was going to be and guess what, by age 26-28 I had not grown any taller....

but I had broadened out, my shoulders and such grew.
Growth plates are not only about your height. Im not the skinny kid I was in my 20s with narrow shoulders.
Your comment on diet is funny and also familiar. I didnt think diet did me any good. I could eat whatever I wanted when I wanted and nothing ever changed, except after 20 years of not working out I got fat but even when I worked out 5x a week for years I could not get Big....
Not until I found this site and learned how to eat properly. I lost 40+ lbs of fat and gained 25 lbs of muscle. Nice trade off I think.