Explanation

• A Septuagenarian is a person who is in their 70s, i.e., between 70 and 79 years old.
• Octogenarian: A person who is in their 80s, i.e., between 80 and 89 years old.
• Nonagenarian: A person who is in their 90s, i.e., between 90 and 99 years old.
• Centenarian: A person who is 100 years old or older.