Is there a way to use I use apps that have blocked their iOS 12 versions and now require iOS 13 on my iPad Air?

Older apps are NOT blocked.

They either been upgraded/moved up to a newer iPadOS version or the older,,legacy versions have been intentionally removed, by the same 3rd party app developers from the Apple iOS App Store server

And yes, your 2013 1st gen iPad Air is becoming obsolete.

Whatever apps that iPad still has on it will still work, as long as these apps work independently of an Internet connection OR are NOT apps that are actually just “app portals” to an actual Website location.

The 2013 iPad Air 1 ( “A” model number A1474/1475/1476 ), iPad Mini 2 ( “ A” model number A1489/1490/1491 ) and the 2014 iPad Mini 3 ( “A” model number A1599/1600/1601 ) cannot upgrade beyond any version of iOS 12, currently at iOS 12.5.5.

Sorry.

These iPad models have overall internal hardware that is too old, too underpowered and incapable of running all of the new, advanced and internal hardware resource intensive features of iPadOS.

These iPad models are now 7 and 8-years old, in 2021.

Sorry.

Third party app support, typically, continues for 2-3 years AFTER Apple ends full support of a subset of their devices.

The last major update to iOS 12 was in 2019, with iOS 12.3.

So, it has been nearly two years after, already, and third party app support is already on a downward trend for all iOS 12 supported devices.

Look for many more third party apps dropping support for all iOS 12 supported devices as another year progresses.

The immediately above statement is what you really need to worry about.

Sorry.

There is one last thing you can try/attempt, if you need to recoverolder versions of apps, for old or older, aging iOS devices.

If you own another much newer iOS device that can run iOS/iPadOS 13 and later, you can install the most recent version app/s onto that more recent iOS device.

Then go back to your older iPad, open the iOS App Store, go to the Purchases section of the store app, search for the app/s you wish to try and download to that older iPad and see if an older version of the app is allowed to be downloaded/installed to that older iPad.

These newer iOS/iPadOS devices must use your same Apple ID user account and password.

Failing that OR IF NO joy, then there is nothing more to be done.

It's 2021, now.

If you need/want an iPad with an up to date iPadOS with access to current, updated apps, then you really need to seriously consider a purchase of a new iPad model OR a much, MUCH “newer” and less expensive, refurbished or used iPad models, from better known, trusted sources, like other Apple product/device retailers/resellers, some locally or from online, on the Web/Internet, capable of running the latest iPadOS versions.

There are PLENTY of newer, older iPad models that can run the latest, current versions of iPadOS.

If you need OR ONLY able to purchase older, less expensive iPad models, look at older IPads from 2014 and later.

All of these older model iPads below CAN run the latest releases of iPadOS 15.

2014, 9,7 inch screen iPad Air 2 models

2015, 7.9 inch screen iPad Mini 4 models

2015-2017, 12.9 inch screen iPad Pro models. ( 1st gen Pencil support )

2016, 9.7 inch screen iPad Pro models ( 1st gen Pencil support )

2017, 10.5 inch screen iPad Pro models ( 1st gen Pencil support )

2017, 9.7 inch screen iPad 5th gen models

2018, 9.7 inch screen iPad 6th gen models ( 1st gen Pencil support )

2019, 10.2 inch screen iPad 7th gen models ( 1st gen Pencil support )

2020, 10.2 inch screen iPad 8th gen models. ( 1st gen Pencil support )

Get the largest internal data storage model you can afford as NO Apple iOS device has ANY expandable storage.

I am sorry that you had to learn all of this, but this does not change any of the facts regarding these older iOS devices.

Sorry & Best of Luck to You!

If you decide to go down the path of purchasing used, secondhand Apple devices, here is how to avoid purchasing an Apple iOS/iPadOS device with user activation lock, in the future.

If you purchase any iPad, or any Apple iOS device, for that matter, used/second hand, online, or even in-person, make sure this iPad does NOT have user activation lock and has been properly reset for sale.

A properly reset for sale iPad should initially power up to an animated, multi-language “Welcome” screen.

DO NOT take the iPad seller's word that this iPad is user activation lock free!

We have seen plenty of used iOS device purchasers get scammed.

User Activation Lock can never be bypasss, circumvented or worked around IF there is no correct previous/original user information to be able to do so.

Apple doesn't get involved with ANY user activation locked, used/second-hand sold devices, either.

So, buyer beware.

If purchasing a used device in-person, power the iPad ON

If the iPad DOES NOT display the initial animated, multi-language “Welcome” screen, then pass on purchasing this iPad.

If the iPad powers up to any other screen, then forget purchasing this iPad.

You cannot trust that the seller actually has the correct needed info to properly reset the iPad back to factory settings right then and there before the actual purchase and exchange of money for the iPad, in question.

Pass on the device!

If you are purchasing this used iPad online ask the seller to provide multiple images, either online or be sent to you via email, showing this animated, multi-language “Welcome” screen of the interested in purchasing iPad model.

Even better, ask for a short video be sent to you showing this animated, multi-language “Welcome” screen, in action and in its entirety, posted to the online ad or emailed to you.

If the online iPad seller refuses any of these requests, pass on the iPad. DO NOT buy!

Good Luck to You!

You can just keep using that iPad.

My wife and I still old 2011 and 2012 iPad models that still charge and still have older apps on them that still work and function as they should.

But third party app support will still continue to dwindle into 2022.

Also, I like to add, by 2022, Apple and third party apps developers have supported your 2013 iPad Air st gen for 9-years!

Apple STILL supports your 2013, 1st gen iPad Air with security updates!

That is why iOS 12 is up to iOS 12.5.5, when the last major update was iOS 12.3.

No Android or Windows tablet will be supported for ANYWHERE this long.

So,, there is that to think about.

Good Luck with that new Android an/or Windows tablet.

You say you’re a former iPhone 6 owner. The iPhone 6 was released by Apple in 2014.

You are currently an original iPad Air owner. This iPad was released by Apple the year before the iPhone 6.