Yes, ANCIENTS is a Scrabble word!

Letter values in Scrabble US: A 1, N 1, C 3, I 1, E 1, N 1, T 1, S 1.

Is it a valid word?

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

people who lived in times long past (especially during the historical period before the fall of the Roman Empire in western Europe)
a very old person
a person who lived in ancient times