If it still gives you a kick to the throat, vape it. I've vaped juices up to 4 years old if I'm remembering right. No problems here. I've vaped some very old juices lol. If your worried about the nicotine shelf life, it'll last till the last drop basically. If your worried about mold or other problems related to the flavorings or the VG/PG... That i'm not sure of. If it has developed floaty molds or if its got anything in it that looks like its not supposed to be there, I'd say its lived a good life and its time to let it go down the porcelain bowl. But I have vaped some very old juices and the nicotine never went bad. PG is a sterilizing agent so I'd have to guess it'd be hard to wait for the flavorings to become majorly contaminated by degrading considering there is such a small opening in the tip of our bottle noses and no air (filled with mold spores) can get in. Bacteria doesn't really stand a chance against the PG and the nicotine.