Final answer:
The statement is true; a third-class medical certificate for a pilot under 40 expires at the end of the last day of the month, 5 years after issuance, making it valid until midnight on August 31, 5 years after the original issue date for a 19-year-old pilot.
Step-by-step explanation:
The statement regarding the expiration of a third-class medical certificate is true. For pilots who are under the age of 40 at the time they undergo their medical examination, a third-class medical certificate indeed expires at the end of the last day of the month, 5 years after it was issued.
Therefore, if a 19-year-old pilot obtained their medical certificate on August 10, it would be valid until midnight on August 31, 5 years later, according to the Federal Aviation Administration (FAA) regulations.