I bought some butternut squash 2 months ago (i still have it) and I read it can keep for 5+ months. Is this true?

5+ for sure, with emphasis on the plus. They keep easily into spring for me. A root cellar, which ideally should be cool and humid, is not the place, however. I keep mine in an unused bedroom, where it is cool and dry. They sit next to the onions, which like the same climate. Go upstairs, not down!

I agree, I've been able to keep mine for a long time too with n o problem.

Yes, they keep a really long time! Same goes for pretty much any hard winter squash. Not sure about the 5 months, though - maybe in a very cool, dry environment, like a root cellar.