But, you can continue to collect them and sell them on Ebay.
Seriously though, the 6-month guideline applies, as Diane indicated, pretty much everywhere in the world. I once made a trip with a passport due to expire in 7 months. By the time I would have returned, it would have been inside 6 months. While not denied boarding, nor experiencing Immigration denials, the Imm officials reviewed all my travel docs very closely and politely advised that I renew before attempting to return. Only took two 2 hours out of my vaca!