How to transfer data from one old ipad to another old ipad (not a new one)

These support pages should get you started with setup of a “new” iPad - and the methods of transferring your data from source to destination iPad:

Set up your iPhone, iPad or iPod touch – Apple Support

Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support

Use Quick Start to transfer data to a new iPhone, iPad or iPod touch – Apple Support

If the donor/source iPad, from which you are transferring your data precedes iOS12.4, QuickStart will not be available.

“Transfer” is rather a misnomer. In reality, your data and setup is merely cloned to the other device. Nothing is moved or removed from the original device.

An alternative is to restore either an iCloud or iTunes backup to the destination device:

How to back up your iPhone, iPad and iPod touch – Apple Support

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

To clarify:

• the transfer process requires that the target device is fully reset.
• QuickStart will not be available if either device has any version of iOS preceding iOS 12.4
• the transfer process can only be used when both devices use the same AppleID