How can I delete old emails to free up iPad storage?

Go to Mailboxes and in the left hand column you will see the main boxes that you can edit. On my MacBook, I go to Inbox and delete any emails that don't interest or concern me by deleting them en bloc by tapping 'Select all', in which case all emails will be erased, but if there are some you want to keep, just tap the empty circles to the left of each email you don't wish to keep, then in the bottom right corner is the Delete button. Tapping that will delete those emails you've selected. There may be. a lot of business emails you wish to keep. Move them to the Archive file.

When you have done deleting, then the fun starts. Scroll down the files until you see all the emails in the Junk tray.

All the junk mail will appear in the right column. Then, tap all the email empty circles, then tap delete as before.

After this, all deleted mails will then appear in the Bin tray shown as a trash bin. Delete all of those.

Getting rid of your unwanted emails will help in keeping your iPad running faster. If you have any iCloud storage (5 Gb is free) try to keep it that way because whatever amount you have, will account for all your devices. I own 3, so I'm careful to keep it below that 5 Gb. As a general guide, 25000 standard email will take up 25,000,000 kilobytes or 2.5 Gb.

Standard means no attachments like pictures, photos or diagrams. The more of those means larger emai space used.

You're welcome, but it's easier to delete on a MacBook or iMac. iPads are ok, but not as good as iMacs or MacBooks.

There are 2 ways to delete emails quicker than I advised.

In the Mail app, tap on a message you want to delete. All of your messages in that category from this sender will appear in a message list. Tap the More button. 

Delete multiple messages at once: While viewing a list of messages, tap Edit, select the messages you want to delete, then tap Trash. To select multiple messages quickly, swipe down through the checkboxes.

You can also enlarge or decrease the size of text to suit your reading style.

https://youtu.be/9qXF9W5etZk?si=z8YhjFEAtggdy3Er

Excuse the British dialect in the video. Just tap the link to watch the video.