Yes you can put a whole avocado in the freezer and it will be just fine.
Then just thaw it out at room temperature when you want to eat or use the avocado.
The texture of the avocado may change a bit as well as the taste but it's okay to freeze the whole avocados.
When freezing avocados it's best to slice or chop up the avocados first and then freeze them as they will remain fresher that way.
But if you want to place whole avocados in the freezer they will be just fine.
Whether the Avocados are frozen whole or sliced up or chipped up the Avocados will last for up to a year or longer in the freezer.
But after 6 months the Avocados won't be as fresh so it's best to eat the Avocados within 6 months or before.