Won't install on Kindle Fire HD Version 7 (OS 5.7.1.0)

Hi, just purchased a Kindle Fire HD 10, 7th Gen for my son and its running OS 5.7.1.0. I cannot get Minecraft to install on it, not from the AppStore or the Google PlayStore. 

I have another Fire 10 9th Gen running OS 7.3.2.9 and it works fine off that.

Any help would be appreciated.

Thanks