The greatest in length or duration; longest.
この橋は町内で最長の歩道橋だ。
This bridge is the longest pedestrian bridge in the town.
彼とは最長で五年間一緒に働いた。
I worked with him for a maximum of five years.
このコースは距離が最長なので、体力が必要だ。
This course is the longest in distance, so it requires stamina.
Having the greatest age or the longest tenure (i.e., the oldest or most senior). Often expressed as '最年長' in everyday use.
部署で最長なのは田中さんで、入社歴は三十年になる。
The most senior person in the department is Mr. Tanaka; he has been with the company for thirty years.
年齢を強調するなら普通は『最年長』と言うが、書類では『最長』と表記されることもある。
If emphasizing age people usually say '最年長', but in documents it is sometimes written as '最長'.