Can’t pair up ipad4 to a ipad9

That is NOT how it all works.

Sorry.

Your 2012, 4th gen iPad is too old to use the newer iOS/iPadOS Quick Start feature.

The Quick Start feature requires an iOS/iPadOS device that can run iOS 12 or greater.

For you to transfer your very old, 2012 iPad 4th gen data to your new 9th gen iPad requires the use of Mac computer or Windows PC.

No other option/s.

If you have access to a full computer, like a Mac or Windows PC, try either using the Finder on a Mac that has the newest macOS Catalina, or later macOS, installed OR with an older Mac with an older Mac OS, download and install the latest iTunes version ( or latest iTunes for Windows PC ), make sure the Mac or Windows PC is connected to the Internet, connect your iPad by the USB charge cable to the computer and let the iTunes application, to do a device data backup of your 4th gen iPad, then disconnect your iPad 4, connect up your new iPad 9th gen, follow all instructions and when asked to restore from a previous backup, choose the recent dated backup you just created from your iPad 4th gen.

Tap the Apple Support article link below.

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

Make sure your iPad is, at least, charged to 50% or greater to attempt this.

Also, make sure your iPad has, at least, between 6-8 GBs of free internal data storage space for downloading and installing a major iOS/iPadOS upgrade.

Make sure your desktop/laptop computer has plenty of internal drive storage space, also.

If NO access to a Mac or Windows computer, you will have to seek help from a good friend or family member, with a full Mac or Windows PC, to help you out

OR

Search online to locate and call contact your nearest, “local” Apple Store location to try/attempt to make an appointment to get your Apple iPad upgraded/updated to its latest iPadOS 15 version.

OR, alternatively, use the “Support” link, in the top black menu bar, at the upper right hand corner of every Apple Support Community Webpage to attempt to schedule an appointment with your nearest Apple Store location.

Apple Store employees will be glad to help/assist you.

Be advise that the backup and restore does NOT restore the actual apps on your devices.

You will need to go to the iOS/iPadOS App Store on your new 9th gen iPad, tap the small circular ID icon, at the far right corner of the main App Store page. A smaller pop-up window appears.

Tap Purchases and attempt to redownload, new/er, up to date versions of all previously purchased/downloaded older apps.

This Apple support article link may, also, help you with using a very old iPad to setup a new iPad.

Set up your iPhone or iPad - Apple Support

Best of Luck to You!