Aviation Medical
Pilot certificates never expire, however, in order to exercise the privileges of being a pilot you must have the appropriate medical certificate for the type of flying you will be engaging in and medical certificates DO expire.
Do You Need A Medical Certificate To Take Lessons?
No, you do not need a medical certificate to take lessons. As long as you are with your CFI a medical certificate is not required. You will need an aviation medical in order to fly solo and/or act as pilot in command after you earn your private pilot certificate.
Get Your Aviation Medical ASAP!
There are many conditions and past diagnosis that can make it difficult or impossible to obtain an aviation medical. Before you get too invested in your training it is best get your medical exam out of the way so that you know you will be able to fly solo (which is required to earn your certificate).
You can visit the FAA Medical Certification page for more information, but, I highly recommend making an appointment with an Aviation Medical Examiner (AME) before filling out any paperwork. You will have to provide a comprehensive medical history of all conditions experienced at any time in your life, so it is important that you answer correctly.
Types Of Medical Certificates
There are 3 types of medical certificates based on how serious you are about flying. Once you have held a medical certificate, you are also eligible for Basic Med which makes medical compliance much easier for the GA pilot.
1st Class Medical - This is the most stringent medical which is required for Air Transport and other commercial pilots. It also has the shortest expiration time.
2nd Class Medical - A little less stringent, this medical is appropriate for a commercial pilot such as a CFI.
3rd Class Medical - Least stringent and most appropriate for general aviation and student pilots. No commercial pilot privileges allowed.
For a more detailed explanation Sporty’s has a great summary of medical certificates.