Erasing an old device

That would largely depend upon why the iPad is not in your possession. If the iPad is lost or stolen - and the Activation Lock (i.e. Find My iPad was enabled prior to its loss), then you may be able to trigger a remote erase.

Here is Apple’s advice for lost or stolen devices:

If your iPhone, iPad or iPod touch is lost or stolen – Apple Support

Use the Find My app to locate a lost or stolen device – Apple Support

If you have sold the device to a new owner, if properly prepared prior to the device being handed to the new owner, then you have absolutely no access or control.