I think the first piece of advice that I shouldn't have to submit is of course...don't do it at school.
Yes, in theory it is legal for you to open carry at the age of 18. In theory it is legal for me to do it at 35, but I still get stopped by police all the time. If you are not comfortable with that level of scrutiny, I would advise against it.
Stay out of Denver.
Do not ask police officers for legal advice, they are almost always the worst source.
Seek the council of a lawyer who is well versed in Colorado firearm law. If you need a number, I can recommend one.
Make sure your motives for your activity coinside with your intent.
That's what I got for now.