What is the superative of 'senior'?

How do you want to use the superlative?

to refer to the oldest man

most senior

Senior is most often used to refer to rank, or someone who has served the longest.
He is the most senior partner in the firm. (Other partners may be older.)
You must present yourself to the most senior officer in the Army. (The highest-ranking, not the oldest.)

In some establishments there may be more than one person with a 'senior' job title, such as 'Senior Partner' or 'Senior Teacher'. In such cases, there may be one who is senior to all tthe others, and s/he is the most senior.

However, in other establishments`there may be one person who is clearly senior to others, who do not have 'senior' in their job title. That person is simply th