It looks like it could be a nipple to me, too--and they aren't always perfectly symmetrical, especially in the boys. I think if it were me, I'd just keep an eye on it for a while and see if it changes at all. If it does change, then make an appt. If it doesn't, we'd likely just mention it next time he went in for something else and have them look at it then.
Don't forget to measure it--sometimes tissue is so slow-growing that unless you've gotten a baseline measurement on it, you can't tell if it's actually changing or not...
