Why does my Apple Account restrict certain downloads on iPhone?

Re: "I borrowed my Apple ID account for someone to download a paid game that my device failed to download.

Why is my device not downloading?"

Could be any one of several possible reasons, and we have little information to go on.

Eg: See if something below rings true in your case.

There may (or may not) be parental controls in place.

If needed: You could check with a parent or guardian

or

See if Apple Support's online article can help you with your settings:

Manage App Store purchases, settings, and restrictions on iPhone - Apple Support

or

Apple requires there is a payment method in an account for the first time you use the App Store oriTunes,

This requirement applies even if you only download free apps.

or

Some apps / games / have age-restrictions that need to be met before you can download them.

You can usually check this in the App Store & etc. before purchase