Another question that frequently comes up for student pilots is the definition of a different class medical exams.
Class I medical exam is for airline transport pilots. For airline transport pilots less than 40 years of age, this physical examination is good for one year. After 40 years of age, the airline transport pilots must have a physical every six months. Airline transport pilot's attaining a Class I physical must have one EKG at 35 years of age, and then one per year after age of 40. These must be performed in the AME office and transmitted to the FAA.
Commercial pilots who are other than ATPs require a Class II physical. This certification, is only good for one year, regardless of age.
Class III physical examinations are for the general aviation pilot. For this process and 40, this physical exam is good for five years. After age 40, the pilot flying is a private pilot only needs a physical every two years. (Hint: If a pilot gets their exam at 39 years, 11 months and 20 days of age, the next physical is due just before their 45th birthday.) Basically if the pilot is not flying for hire, all that is needed is a third class medical.