Many characteristics humans are wired to find attractive are indicators of youth and coincidentally markers for health as well. There are evolutionary advantages to this, and nothing in the recent (in historical terms) societal decision to push the age at which we consider attraction "healthy" upwards towards 21 has changed this.

Large eyes, small nose, slightly larger head, long legs, smooth skin (unblemished and unwrinkled), small waist and so on are all characteristics that are attractive to a large percentage of humans (male and female). If taken to an extreme they tend to appear childlike because they are factors that indicate youth. Finding these things attractive is not an indication of an attraction to children, simply an attraction to the markers of youth and health that for the vast majority of the times humans have been on the planet were a huge evolutionary advantage.

This is, for example, one of the reason Asian women hold such an attraction in the west... they tend to hold more of these markers later in life. For any given age to western eyes they look younger than a western counterpart would. It is no surprise that in comics and anime these characteristics are exaggerated - and it is not a surprise that such exaggerated features are largely considered cute and attractive or erotic. The line / mix between eroticism and innocence is well known.

It may squick some, especially in the current climate of hyper political correctness where more and more often western society, especially in the US, is trying to deny that anyone under 21 might (god forbid) be attractive. But that wont change human nature, and it doesn't indicate illness.

The Girl has the body of an adult - that she has the facial and other markers of youth is not really going to change that - it just makes her more attractive to more humans for reasons that are beyond or below societal and political dictation.