Depends. If you are 1500 and looking for basic ideas, they are fine. If you are 2000+ and looking for the latest novelty, or to avoid the latest novelty for your opponent, then yes, 12 years for an opening book is like trying to win an online first person fighting game using Windows 95 and 64 KB of memory.
Old(er) Opening Books

lol , i use a botvinnik semi slav book from 2000 and even there I do fine with it. Even if I play an outdated line, whos going to remember its refutation?
I wouldnt worry too much, people below master level rarely follow the latest theoretical developments.

lol , i use a botvinnik semi slav book from 2000 and even there I do fine with it. Even if I play an outdated line, whos going to remember its refutation?
I wouldnt worry too much, people below master level rarely follow the latest theoretical developments.
I do. The Queen sac line on g7 is no longer best for White.
Also, the Catalan has gone thru many updates in the last 10 years.
A better example of an opening that hasn't changed is the London System. It was sh*t in 2000, and it's still sh*t today!

I have also older books, one is Batsford Chess Openings 2 (1989) but I have used lately an explorer in another chess service.

Some books are EXTREMELY outdated, but there are sometimes extremely rare lines that are completely forgotten, and then interesting play results...
Most are useless. There are some books that are good, (there is one old endgame book, can't remember, and too tired to check.)

To the people who say it depends on the strength of the player using the repertoire, and the topicalness of the lines, here : I'm ~1900 CFC (equivalent to...well, 1900 USCF) and I'll probably be playing against a lot of players ranging from 1900-2100. Attacking with 1.e4 is a repertoire book for White that recommends less theoretical lines like Closed Sicilian, KIA, Bishop's Opening and 2.c4 Caro-Kann. I imagine it'll still be fine to use this book for my repertoire. Play the ... as Black is repertoire book for everything after 1.e4 e5 except the Ruy Lopez, based around the Two Knights Defense. Most of the more recent books and DVDs I've seen recommend 3...Bc5 against 3.Bc4, but I personally prefer 3...Nf6. Idk if the aforementioned book is highly outdated by now...

If the book is authored by Bellin-Ponzetto or King-Ponzetto, then it is still more relevant for any under-IM player than the latest QualityDump or Everynut waaaaay-too-annotated theoretists' jewels.
Older books with some didactic and explanatory elements to them are generally still very good today, even when they treat openings.
Are opening books from 12 or so years ago (ex. Attacking with 1.e4, Play the Open Games As Black) outdated by now? Can I still successfully use the theory given in them?