Are you acting on these drafts in any way? Mailing, message, etc.? If you are, set your processing actions to automatically archive or trash the draft after success (related docs) so they just go away.
If you just want to periodically clean up old drafts to cull the inbox, take a look at the Inbox Sweeper example action.
Note that you can act on multiple selected drafts as well. On Mac you can command or shift click to make multiple selections in the draft list, and secondary-click for a context menu with many options (like archiving/trashing). On iOS, use the “Select” button to enter select mode, tap drafts to select them, then use “Operations” to act on all those selected drafts.