You may or may not believe this as a ranking factor. If it is not the factor for ranking why would the google play store ask you for the age restrictions. Indeed this is also one of the elements for determining your application ranking in play store. The Google policy has clearly defined in its policies that the age restrictions is one of the important parts of listing. Applications that are not suitable for the age group below 13 years, 3 years will not be displayed to the audience who fall under these groups.