the same thing happened before in my military days, my arms are kind of short, so when I was really fit, even with stretching and yoga, I have limited range of motion, my friend is a yoga instructor and was kinda shocked. I can't upturn my palms fully either, it's frustrating

still doesn't mean you will have 18-20 inch arms with a couple months of training or bulking phase man.

I'd work on stretching also, might not have immediate results but should over time. I couldn't get my fingers under the bar to front squat so had to cross my arms for a while. Now I can after a couple weeks of stretching.