Needle size

Hi all, I'm about to do my first injection cycle and would like to know if 13mm needles were long enough to reach the gluteal muscle. I don't plan to inject anywhere else. I have 10-11% body fat and I'm pretty dry ( not much fat ). Will this do or should I use 25mm needles as a precaution? I've seen insulin needles that are 13mm and 30g (which would be better for me psychologically as I've never injected), so I'd like to know whether it would be good or not.