Karate - what do I need to know?

Hi all, I'm thinking of starting Shotokan Karate. I have not done any martial arts training before and I'm unsure of what to expect. I have no desire to knock anyone out or before a master. I'm 6'4" and 46 y/o - old enough and wise enough to know how to diffuse trouble if I need to (generally). I'm interested in Karate as a sport/relaxation/club thing. I've always been interested but I don't know what to look for in a dojo or a sensei or what questions to ask? Am I too old? Will it be too much contact? Should I look at a different form of MA? Any help would be appreciated :)