As an alternative suggestion, what if we could tag specific content warnings?
For example, I don't put Errant as "mature" because.... well, it's so clean some people seem to think it's for children? (yeah, nah, it's not), but it does/will contain:
Consumption of Alcohol
Violence (including some blood and things like limb loss on magical beings)
VERY Mild cussing like "damn" or "hell" (I tone this down and avoid words like "shit" specifically because I don't know where the line is drawn on language and mature ratings)
Jokes about and allusions to sex (but it won't contain nudity or actual sex scenes)
So really I'd either like to be able to tag that this is a roughly PG13+ or 15-rated comic, OR to put in some tags like "yo, these people might hit things with swords and also they are British adults and they would like to drink beer and make some naughty jokes after a long day hitting things with swords.
Some DVDs and Games have a little chart with the rating that shows whether it contains:
Language, Nudity, Violence, Drugs/Alcohol
and to what degree. Maybe that'd be more useful, since I get that with an international audience and creators, it'll be hard to agree on what's good for specific ages. Naruto contains all the same things as my comic; alcohol, blood, mild swearing, sexy jokes, and in Japan is a shounen manga aimed at about 11-15 year olds, but in the west it's labelled a solid 15 unless censored.