(f) No person shall carry concealed on or about his person a or dagger, dirk, stiletto, bowie knife, commando knife, any blade of which is released by a spring mechanism, including knives known as "switch- blades" or any other type or kind of knife, any blade of which is more than two and one-half inches in length, ordinary razor or other dangerous weapon except that no person 18 years of age or under shall carry concealed on or about his person, any knife, the blade of which is two inches in length or longer. Provided, however, that this provision shall not apply to the following officers while engaged in the discharge of their official duties: sheriffs, peace officers, and corrections officers; nor to the following employees or agents while engaged in the discharge of the duties of their employment: conductors, baggagemen, messengers, drivers, watchmen, special agents and policemen employed by railroads or express companies; nor to persons lawfully summoned by an officer to assist in making arrests or preserving the peace, while so engaged in assisting such officer.