How to delete old email on iPhone and iPad

You can’t select or filter emails by date on an iOS device in the built in mail app other than by adding the Today option to the app. If you add a Today Mailbox, that will filter by the day’s current emails. You can add that by tapping Edit at the top of the main Mailbox pane and then select Today. Tap Done when finished. Today’s emails will appear in that mailbox.

You can’t. I said that in the first part of my response that you cannot filter by date other than the Today option.