old boy

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Chiefly British A graduate of a public school for boys.
• noun A man who is a member of an old-boy network.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun chiefly UK An alumnus, especially of a public school.
• noun UK Affectionate term of address for a man.
• noun A former member of a group

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a former male pupil of a school
• noun a vivacious elderly man
• noun a familiar term of address for a man