I didn't pin shoulders till I was 100% sure I could fit 1.5" pin in there.
I probably could have started from day 1, but was just scared. I mean I've had it done by nurses before for IM injections of immunizations, but something about oil going in there freaked me out.
Anyway, I pin quads only nowadays, and only 2cc's in each 2ce a week. But shoulders are OK for 1cc, quads are good for I think up to 5cc's! Never done triceps, but my buddy swears by it. Really, you can pin anywhere you like as long as there's muscle and not many veins/arteries in the area. Also watch for nerves, you get a "kick" in the teeth when you nick them!