I. noun
1. usually capitalized O&B : old nick
2.
a. : an often sprightly or waggish old man
that incorrigible broth of an old boy — Peter Forster
b. : a man of a past era or of established prestige
not in the nature of these tough old boys to give way — O.S.Nock
I find the old boys … too long-winded — O.W.Holmes †1935
3. chiefly Britain : a graduate of a boys' school : alumnus
heard a headmaster say that the test of a school was the quality of the old boys — Manchester Guardian Weekly
II. noun
: a man who is a member of a long-standing and usually influential clique especially in a professional, business, or social sphere