I wouldn't worry about it, actually erections with out purpose are a normal part of 19, 20, 21... etc. until you hit the age where you have a more relaxed penis, it just happens - your still sexually maturing as a male, I think almost every male that is over 30 knows all about this phase - so for older guy, it's just like, yep been there done that, so you might get more sympathy or just people ignoring it then not - most likely the only commentary or notice will come from guy your own age that are either in the same phase, or are vocal about it out of lack of disgression or ignorance that it's a normal thing... all in all, just be yourself - hard or soft...lol.