Sony has listed The Last Guardian on its online PlayStation Store but there is currently no option available to buy the game.
The page was discovered by NeoGAF and has been screen capped above in case it's removed. It seems that the game will not be released digitally according to the listing which states that it is "Disc Only" though it's possible a separate page will be posted for the downloadable version.
The Last Guardian is listed as having a age 12 from PEGI, the European version of the ESRB, which does not appear to be provisional suggesting that it's already passed the classification process. If so, it would suggest the game is nearing release.
In November Sony Japan Studio head Allan Becker said The Last Guardian was "moving in the right direction" while later that month the game's creator Fumito Ueda commented that he was "terribly sorry for that for various reasons I have kept my audience waiting for such a long time".
Ueda depated Sony in late 2011 and has since worked on the project as a consultant. The Last Guardian was first announced at E3 in 2009.