As some of the comments above have stated, I'm also a huge fan of forgoing age based categories and focusing more on specific content warnings. This will make it easier for people who are comfortable with one type of "explicit" content to filter results to show games that they're more likely to feel comfortable playing and enjoy.
Potentially losing a section of an age group that would enjoy your content just because it's labeled 16+ or 18+, or thinking that the content will be watered down just because it's 13+, hurts both players and developers.