Yes, you can edit descriptions from your old pins:

• Pinterest descriptions give your Boards and Pins more context. They provide Pinterest users a hint about the type of stuff they'll come upon. Pinned to your Pinterest boards,
• Register for a Pinterest account.
• In the top-right corner of your screen, click your profile image.
• If you saved the Pin to a board, then to a section, click inside it.
• To open a Pin, simply click on it.
• Select the ellipsis icon from the drop-down menu.
• Select the Edit Pin option.
• Click Save to save your changes to the Pin's board, section, title, description, website, alt text, and note to self.
  
  
  

Read More: What’s another way to show you pins to your audience without always linking to Pinterest?