I'm 5' 9" and 149 at about 10% BF. Serious ectomorphic tendencies.
That's at almost 50 years of age. When I was 30, I was about 160 at 7%. Still a runt compared to most of you, but I still had a noticeable weight-trained look.
BTW, I had dropped to less than 140, and HST seems to be helping bring back the "young me." After 2 cycles, I've gained some significant upper body mass--having trouble fitting in to some of the sport coats I bought a couple years ago.
Now if I can work around these stressed out knees, and bring the lower body along. If it can be done, I'm betting HST will be the way...