Mine are 18.5 flexed but cold, just under 5'9" and 10% bodyfat. The other day I measured them pumped and they were almost 19.5, I wish they were that big all the time. It really does boil down to proportions though. I get constant comments at the gym, no one believes my arms are under 20", but since my frame is so small they look much bigger.
Being a skinny kid sucked when I first started, but after 12 years of training its starting to pay off....