I've never had any issues with law enforcement, and very few with people I come across... none at all which weren't turned into a positive encounter by being polite, informative, and articulate. Those few initial negative/leery responses were not a result of my apparent age, they were simply unsure of the legality, and surprised that I was not LE.
I don't OC when I cannot present myself in a clean/professional manner. If I am in a bad mood, or working on a dirty project and have in public to go get some parts or something, or sometimes if I decide to dress like a ragamuffin and not shave, I'll conceal. I realize that I don't have to take that precaution, but, I think that carrying while presenting a questionable appearance or attitude is akin to speeding,using rude sign languageand driving recklessly with a cross or fish symbol on one's vehicle. I'm an ambassador for gun owners, and since all of you will be judged based on how I present myself, and act in certain situations... I want to be responsible.