Marbury took a year off & remember what he looked like? Jason Williams did also plus he is older. Even Michael Jordan didn't come back from a year layoff well & he stayed active playing baseball!
Yeah, that's something to consider, but Jason Williams will have the benefit of going through training camp with the Celtics, and he will probably shake that rust off by the time it gets to the playoffs.
If the other free agent options are Royal Ivey, Tyronn Lue, Brevin Knight, Anthony Johnson, Anthony Carter, Jason hart, where do you think he would rank among those players?