I talked to a Doctor a while ago who told me that in his interview they asked him about something he did while he was 13 years old (participated in marathons or sth)....the entire interview was him talking about his experience and the interviewers were super interested. He told me that something he did as a kid literally got him in to medicine (i guess the same applies to dentistry). So I don't think when you do it is a important as what you do. They want to know that they are accepting someone who didn't cram all their EC's and volunteer into the summer before applications...but rather accepting someone who ALWAYS was an all around person.