Q: Anybody found out how to print A4 size from an iPad?

The options that appear depend on exactly what AirPrint printer you are using.

(This screen shot is from an iPhone, but an iPad print to this particular printer would show the same content.)

As you can see, my printer does not offer an option to change paper size either.  But I can change other things, such as whether or not to print double-sided.

I Have an HP PhotoSmart 7520 and HP has an iOS app that allows you to select different paper sizes. I have never needed to print A4 size, but the option is in the printer app settings. You should look to see if your printer has a similar app.

Following on to @Demo's comment:

I have an Epson WorkForce 645 as shown in my first response.  I have the Epson utility (Epson iPrint).

Interestingly, Epson iPrint does allow choosing a scanned paper size, but not an output (print) paper size.

It could be that I am wrong then. If you look at my screenshot, it is a Scan window in the tutorial. Like I said, I have never printed the A4 size. It may just be for scanning like your app.

I understand, thanks.

I also have never printed A4 size.