Out of Casas, Grissom and Story, the only one that's had his 25th birthday is Story, so I don't think age is a factor here.
Casas - his injury is of a type that makes us all nervous, no question. May have to do with why they seem to be actively shopping him.
Grissom - Mr. X - the odds don't seem great he's a long-term Red Sox player, but they have to give him a shot.
Story - have to give him his shot too. Sale-esque situation.
I don't think the Sox are really counting on any of these 3 as locks to be healthy and productive.