I have an app called 'Sexgame' in the Play Store. It is rated 17+ in the US. The app can not be found searching for 'sexgame' in the Play Store. I already have two other apps in the Play Store that are among the first results, when searching for their name. When searching for 'sexgame', other apps rated 17+ show up among the search results. I conclude by this, that apps rated 17+ are not generally filtered from search results in the Play Store.
Another explanation I can think of is that apps with certain names are censored. My apps name contains the string 'sex'. Is it possible, that this is the problem? Although I think that 'Sexgame' describes my app pretty well, it doesn't suit me if nobody can find it and I'm thinking of changing its name. Before doing so however, I would like to confirm that Google does censor certain words in app names.