I reuse bottles. I've been using some of the same bottles since my first-born was a baby. I use glass, though, and buy new nipples and throw the old ones away after each baby is done with them. Glass is good forever. When it comes to plastic,.... I'd be way more cautious.
My sister used Similac brand bottles for her baby, which got discontinued REAL fast because they were breaking down after just weeks of use, and these poor babies were being fed a bunch of plastic without their parents even knowing about it. The physical sign was little white spots on or in the bottles. So please, if you're using older bottles, look for tiny (or big) white spots, and don't try to wash them away - throw them away. I only say this because when I was given some Dr Brown's bottles, they had white marks inside, which the person told me to just wash away, but I had experience with bottle breakdown and knew better.
If your bottles look perfect, they're probably as safe as any plastic bottle will be, but replace the nipples so they don't tear or anything.