The aimed user for these guidelines are the general public, ranging from teens all the way to elderlies. These guidelines have been perfected based on trial and error, what feels comfortable and intuitive and what doesn't. The aim for this interface is to become intuitive, which has become the case for apple users. However, I think it's taken years for developers and UI designers to train the general public for this to be the case. As far as eligibility, they have very strict guidelines for text, it ahs to have enough contrast with brightness and color, yet not catch your attention too much unless wanted. The size is fixed, yet the user can modify it depending on their needs by making it bigger or smaller. Something that I've noticed as a apple and now android user is that apple is more strict with how much they want the user to customize the interface design, as opposed to android, where they give more freedom to the user to personalize their interface design. The human Interface Guidelines are amazing for the general public, however, it may not be the case for those who are interested in more experimental and exciting interfaces.