noun which may take the genitive case particle 'no'
eldest; oldest
Used to describe the person with the highest age in a group. Often used as a no-adjective before nouns like 者 (person) or メンバー (member).
彼はチームの最年長メンバーです。
He is the oldest member of the team.
最年長の参加者は90歳でした
The oldest participant was 90 years old.