How to Auto Delete Old Emails In Any Gmail Trash

Step 1 - Separate your priority messages from your non-priority messages.

• To do this, you’ll need to click the little arrow near the right end of the search box:
• Gmail will show you advanced search options. Now select the “Doesn’t have” field and type in “label: important.” This will supposedly — we say supposedly for a reason you’ll find out later — select all the messages that aren’t marked as “important” (those are the emails with the little yellow pentagon next to them, in case you didn’t know).
• If you want to save your Gchats too, type in “label: chats” as well.

Step 2 - Move to trash.

• Once you’ve searched for all your chats and non-priority emails, you’ll want to select them so you can move them to the trash.
• To do this, click on the check mark at the upper left. Then click on “Select all conversations that match this search” at the top of your inbox. 
• Your screen should look like the image below. Next, click on the trash icon:
• Click Ok

Step 3 - Do something else for a while.

• If your inbox is near capacity, chances are you’re moving A LOT of messages, and it’s going to take a while. An error message might pop up, but your emails should still eventually transfer to the trash:
• While you’re waiting, why not step away from your computer to make some coffee? Or call your Mom? She’s the best.

Step 4 - Save your important messages from accidental deletion.

• By now, you should be able to find all the messages you wanted to get rid of by going to your “Trash” folder. That’s here
• Once you’re there you’ll probably notice something odd: A few priority messages have been deleted, too. Why this happens to your poor important messages we’re not sure, but a few always seem to end up in the trash, and it’s up to you to recover them!
• Luckily, there’s an easy way to do just that. In the search field, next to “in: trash,” type: “label: important.” Select all the messages and move them back to the inbox, where they’ll be safe:

Step 5 - Finally, get rid of all those ugly messages you don’t want.

• Now with your important messages back in the inbox where they belong, it’s safe to delete all the non-priority ones. Select all the messages remaining in Trash and click “Delete forever”:
• This might take a while, again. Make a second cup of coffee, then get some props from the office dog because you’re almost done:
• Come back to your computer screen and bask in the glory of your tidy inbox