Avocados never get old. Most of us can eat them in some form—whether in a smoothie, on toast, or atop a taco—for breakfast, lunch, and dinner and not get sick of it. But they do, literally, get old. As in, they don't last forever.
You can try to fend off the dreaded brown and preserve the green of a cut avocado by storing it in a shallow pool of water, but if you want to extend its life any longer than just a few days, your best bet for a ripe avocado is the freezer. (For an unripe one, try pickling it!)
Yes, you can freeze an avocado. Did you just become suddenly aware of all the squishy avocados you've unnecessarily thrown out? Yeah, us too. Those things are expensive. But, no longer!