It depends on which state you are in, and whether you keep it in plain view or not.
In WV and VA, anyone who may legally possess a handgun may carry it openly without any sort of permit.
In TN, you must have a "civilian handgun permit" to carry in any manner--Open or Concealed.
Since you are 20, you are not eligible to get a TN permit yet (must be 21). So in TN, you can't carry a handgun unless you are under the direct supervision of your parent or guardian.
But in WV and VA, anyone over 18 may legally OC with no permit requirement.
Just be sure NOT to cover it up or conceal it in any manner, and you should be fine.