You certainly can bump up old threads, if it adds something of value to the discussion or if you're the OP or if you've already posted in it once.
Idk who said it, I think it was Raul.. or one of the old supervisors.
Could also be that none of them said it and memory isn't serving me correct.
Anyway, if you got a thread from 2006 about a incredibly peculiar GBA/NDS/Wii problem for example and have figured out a way to fix it, you can necrobump a thread.
People on google who stumble upon the thread will get an answer from it immediately then.
Tho in general, threads that haven't seen activity in >6 months/ 1 year shouldn't be bumped anymore.