Now

Girooo & Bats are both impact subs at best.
They serve no purpose as starters, at this level under Frank.

Tammy 1st choice, "false 9" second choice...henceforth.

Giroud is an international class striker for one of the top nations in world football, hes not 40 years old as people make him out to be ancient, hes not young certainly but he was on the pitch minutes yesterday and got on the end of a great cross something both michy and tammy would not even been close too, i believe giroud willl score plenty wth reece and mason providing the crosses, hes good with both feet and his head- and lets face it the alternatives Arent cutting it. False 9-who? Willian or Barclay , neither have an end product, mason too important other places, Kante nope. Pedro possibly only player we have that is a direct goal threat from outside the box with either foot.

"he was on the pitch minutes yesterday and got on the end of a great cross"

That's my point and case in point, Giroud is good for being an impact sub. Generally thrives when played as an impact sub.
Maybe Giroud should have got more sub (& cup) appearances, but that's about it.
Cup competitions/tournament football is Giroud' niche.

Whenever he starts league matches impact and goals is non-existent.

Nothing to do with age.
Everything to do with...suitability, speed of play and mobility/intensity pressing from the front leading the line.
Ask him to do any of those starting PL matches and he struggles, showing clear limitations. Can't cope with the demands.

Giroud may be an "international class striker" for one of the top nations, doesn't make him conducive to the way Frank wants to play.