I know croup is common is infants, but is it possible that a 16 yr old could have croup?

Sure: Croup is a name designated to a clinical diagnosis of inflammation of the larynx and trachea. It is caused by many viruses - the most common being parainfluenza. You can be infected with these viruses at any age but the older you are the less likely that you'll exhibit the same symptoms that a younger person will exhibit (seal-like barking cough and inspiratory stridor).

Croup Any Age: Croup is an infection of the windpipe (trachea) and bronchioles. This infection is usually caused by two viruses, influenza (the flu) and parainfluenza. Both cause an expiratory, brassy cough. A person of any age can be affected, and this disease takes a more severe course is the smaller airways of infants. Croup can be very mild in severity in older individuals, but may aggressive in infants.