noun
centenarian
Refers to a person who is 100 years old or older. A formal term often used in official contexts, such as government statistics or congratulatory messages.
日本では百寿者の数が年々増えている。
In Japan, the number of centenarians is increasing year by year.
祖母は来月百寿者になります。
My grandmother will become a centenarian next month.
長寿 means 'longevity' in general, not specifically reaching 100 years.
Compound of 百 (hundred), 寿 (longevity, congratulations), and 者 (person). The term is a modern coinage reflecting the celebration of reaching 100 years of age.