What was the maximum age limit for the first astronauts?

Although the United States National Aeronautics and Space Administration (NASA) planned an open competition for its first Astronauts, President Dwight D. Eisenhower insisted that all candidates be test pilots. Because of the small space inside the Mercury spacecraft, candidates could not be tall. The limit was 5 feet 11 inches (180 cm) and weigh no more than 180 pounds (82 kg). Other requirements included an age under 40. It was the maximum age limit for the first astronauts (1959 Group 1 - "The Mercury Seven"). A bachelor's degree or the equivalent, 1,500 hours of flying time, and approved skills for flying a jet aircraft were required.

As of 2018, there are no age restrictions for the NASA Astronaut Corps. Astronaut candidates have ranged between the ages of 26 and 46 and are required to be U.S. citizens. They will meet education, work experience, and medical standards. They will also complete a very hard two-year training program. Still being an astronaut does not guarantee the person will fly in space. Before being selected for space flights, some have resigned or been medically disqualified after becoming astronauts.

NASA now continues to select candidates from diverse backgrounds and thousands of applications. However, only a few are chosen for the intensive Astronaut Candidate training program. Including the 1959 “Original Seven”, 339 candidates have been selected as of 2018. Civilian candidates go for 5 years; military candidates have specific tours to do.