Yes, SENILITY is a Scrabble word!

Letter values in Scrabble US: S 1, E 1, N 1, I 1, L 1, I 1, T 1, Y 4.

Is it a valid word?

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

mental infirmity as a consequence of old age; sometimes shown by foolish infatuations
the state of being senile

Also: second childhood.