Answer:

oldest

Answer	Crossword Clue
OLDEST	Guinness Book adjective
OLDEST	Most aged
OLDEST	Like a babysitting sibling, probably

OLDEST	Firstborn
OLDEST	Most advanced
OLDEST	Having seniority
OLDEST	Tops in longevity
OLDEST	Least recent
OLDEST	Most passe
OLDEST	First-born
OLDEST	Least fresh

OLDEST	Superlative for St. Augustine, Florida
OLDEST	First born
OLDEST	Jackie, vis- -vis the rest of the Jackson 5
OLDEST	Most ancient
OLDEST	Having the most privileges, maybe
OLDEST	Most senior
OLDEST	Created first
OLDEST	Born first

OLDEST	Senior
OLDEST	Longest lasting
OLDEST	Most ancient.
OLDEST	Most venerable.
OLDEST	Most skilled.
OLDEST	Most mature.
OLDEST	Of longest standing.
OLDEST	Firstborn.

OLDEST	Senior.
OLDEST	The senior.
OLDEST	Least fresh.
OLDEST	First-born.
OLDEST	Most trite
OLDEST	Adjective for Methuselah
OLDEST	Adjective for St. Augustine, Fla.
OLDEST	Like Methuselah

OLDEST	Harvard, among U.S. colleges
OLDEST	Most venerable
OLDEST	Longest-lived
OLDEST	Most antiquated
OLDEST	Describing a doyen