Dr. Gillen grew up in the Palm Beach Gardens/North Palm Beach area. He attended The Benjamin School, which led to his introduction to PGA Animal Clinic. He began working for Dr. Giurato during his junior year of high school, and continued to work during breaks while in undergrad at Auburn University in Alabama. Dr. Gillen earned his Bachelors of Science in Animal Sciences from Auburn University in 2008. He then attended St. Matthews University for veterinary school on Grand Cayman Island, where he completed his first three years.