Yes, STAGERS is a Scrabble word!

Letter values in Scrabble US: S 1, T 1, A 1, G 2, E 1, R 1, S 1.

Is it a valid word?

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

someone who supervises the physical aspects in the production of a show and who is in charge of the stage when the show is being performed
an experienced person who has been through many battles; someone who has given long service

Also: stage manager, old-timer, old hand, old stager.

Not playable in Scrabble US: OLDTIMER.