Yes, EOLITHIC is a Scrabble word!

Letter values in Scrabble US: E 1, O 1, L 1, I 1, T 1, H 4, I 1, C 3.

Is it a valid word?

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

the earliest part of the Stone Age marked by the earliest signs of human culture

of or relating to the earliest period of the Stone Age (characterized by the use of eoliths)

Also: eolithic age.