I've heard all kinds of stories about pitchers over the years. I hear of pitchers that never get sore and I, personally have a hard time believing that. I'm sure they're not lying, but I have yet to personally meet a pitcher who doesn't get sore after a relatively long outing.
Keep in mind. There is a difference between being sore and feeling pain. My son has been pitching since he was 8. I don't remember about being sore during the 8-11 years, but I know that he would get sore at 12+. He still will get sore if he pushes it. My son knows when he is just sore from throwing a lot and when he is feeling some kind of pain, or discomfort other than being sore.
My son played rec league until he was 12. Only played maybe 25-30 games a year between spring and fall. However, he was ALWAYS throwing something. Whether it was tennis balls at the garage door, superballs at the walls in the house, rocks into the lake, whiffle ball games, whatever. Starting at 12 he played travel and if he was up on his pitches, he would get sore. I'll still talk to him and if he goes over 85 or 90 pitches, he'll get sore. Once in a while he ices, but has never really liked to do it much. Fortunately (knock on wood), he hasn't had any major injuries (ie. surgery) and is still pitching at 21 years old.
I just wanted to make the point that there is a BIG difference between getting sore after an outing and feeling pain after an outing. I think sore is OK, pain is NOT.