noun
senior; elder; person older than oneself
Refers to someone older, often in a group or relative to the speaker. Neutral term; can be used in formal or everyday contexts.
年長者の意見を聞くことは大切だ。
It is important to listen to the opinions of one's elders.
彼はクラスで一番の年長者だ。
He is the oldest person in the class.
先輩 refers to a senior in a school, workplace, or organization, based on experience or tenure, not necessarily age. 年長者 is purely about age.
Compound of 年長 (ねんちょう, 'seniority in age') + 者 (しゃ, 'person').