Instead of having a specific age, or age bracket, for games - maybe the game could have a rating score that indicates the general type of content expected.
Blips & Chitz: World of Adventures (7/100)
Murder & Mayhem (83/100)
Weed Smoking Simulator (42/100)
Wholesome Fun: Part 2 (0/100)
For example, you could be fairly granular with content questions and assign them a weight (value). This could be compiled with other values based on the type of content.
Cartoon Violence [None (0)] [Mild (1)] [Moderate (2)] [Intense (3)]
Fantasy Violence [None (0)] [Mild (1)] [Moderate (2)] [Intense (3)]
Alcohol [None (0)] [References (1)] [Usage (2)]
Drugs [None (0)] [References (1)] [Usage (2)]
Gambling [None (0)] [Simulated (3)] [Real (15)]
You could then compound the result to account for multiple items of the list, rather than let the developer directly set their own rating.
ex. Alcohol [References (1)] + Drugs [Usage (2)] would result in a rating score of 3. However, because both drugs and alcohol are involved, an additional 2 points are added; resulting in a final score of 5.
Not sure if this might be more complicated than what you are looking for in terms of implementation and usage.
Additionally, you could then display these warnings somewhere for the game
Pirate Simulator: Swashbucklin' Adventures
Content Warning Rating: 32/100
This game contains
- moderate depictions of fantasy violence.
- references to alcohol.
- mild swearing.
- moderate cartoon violence.