Hello,
First, I would recommend setting the “Clean up recurring events after” setting under Events > Settings > General to 1, which should help keep the number of old recurring events down. There is not currently any built-in functionality to delete all past events at once, but you can increase the number of events shown on the admin page by clicking “Screen options” at the top of the page (see screenshot). This will let you select more events at once to delete. You might also try using a plugin like Bulk Delete or Post Expirator.
If this is a feature you would like to see added in the future, we’d love it if you could post the idea in our Feature Ideas Forum! We use it to gauge user interest in new features and help plan future development. Please let me know if you have any other questions.
Thanks,
Jennifer