old boy

noun

1. Informal. an adult male, especially a Southerner.Compare good old boy.
2. a lively elderly man.
3. Chiefly British. an alumnus, especially of a boys’ preparatory or public school.
4. Chiefly British. old chap.

noun

1. (sometimes capitals) British a male ex-pupil of a school
2. informal, mainly British
   1. a familiar name used to refer to a man
   2. an old man