Yes you can open carry in Colorado at age 18 without a CHP. I wouldn't recommend OC'ing at the mall as most malls are owned by Simon Corp and they prohibit firearms in their malls.
Also along with the city and county of Denver the OC ban extends to all Denver owned or controlled property.
For vehicle carry, Colorado views your vehicle to be an extension of your home. You may OC or CC in your vehicle with or without a permit.
Welcome to OCDO and stop by the Colorado forum here.
For a Colorado forum that covers more than open carry check out cogunowners.com