Yes, OLDER is a Scrabble word!

Letter values in Scrabble US: O 1, L 1, D 2, E 1, R 1.

Is it a valid word?

OLDER is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

advanced in years; (`aged' is pronounced as two syllables)
used of the older of two persons of the same name especially used to distinguish a father from his son
skilled through long experience
(used especially of persons) having lived for a relatively long time or attained a specific age
of long duration; not new
(used for emphasis) very familiar
skilled through long experience
belonging to some prior time
(used informally especially for emphasis)
of a very early stage in development
just preceding something else in time or order

OLDER was the Wordle answer on Sept. 11, 2023 (#814). Stuck on today’s? Use the Wordle helper.

Also: sr., one-time, honest-to-god, honest-to-goodness, sure-enough.