I have seen some people post about how they enjoyed fun, playful, colorful games as a kid, games with abstract worlds, imagination, etc.

But then, at some point their in teenage years their tastes “matured”, and now they could never see themselves playing anything other than “realistic” video games, gritty shooters, sports sims, sex, cursing, gore and war galore action games, etc.

How long does a person hold onto that teenage angst, addiction to intense stimulation, etc.?

When do those tastes evolve past that limited scope of games and start to look at ALL games, regardless of what year it released, artistic direction, etc.?

When do they begin to explore an eclectic spectrum of genres and stop judging excellent smaller budget games, indie games, games with anime, etc. as “unplayable”?

When do they stop worrying what others think of them based on what games they play?

When of they stop worrying what others think of them when they play a handheld console in public, just like every person who games on a phone or tablet?

Should we really even call these  games mature? Would it be more apt to refer to these games by what themes they explore without a connotation of “maturity”?

"Mature Rating" doesn't mean mature. It just means 16/18 due to violence/sex.

No a lot of them aren't Mature. The Last of Us is, Saints Row isn't.

Play what you want, there'll always be people that look down on you for playing any game at all, not just cartoony games.

The game is rated Mature because it contain content that mostly only suitable for mature audience (gore, sex, offensive word, etc). The artstyle doesn't matter. You can have cartoony games with M rating. If most ppl enjoy realistic style games it's up to their preferences but it has nothing to do with the rating.

Your OP title poses a question, but how your OP thread reads it's more like you criticise the so called mature connotation in videogames nowadays instead based on what some teenager players might experience or approach them as they grow older. I'm not sure how to proceed, so I'll just adress the title in the question first:

Some games are, some games aren't. There are certainly games deemed mature that aren't mature at all, save for the specific gore and violence they display. Like Barkley says, the "Mature Rating" from Pegi or ESBR doesn't really deemed the game's themes mature, just that it is a game that children shouldn't play, for one reason or another.

I think referring as to "realistic" gritty games being the only mature games is a mistake in your approach, though. How a game looks like has nothing to do with how mature it is. Braid is a videogame with a specific art-style in mind and deals with mature themes in its approach.

As for the rest of your OP, I don't know. You seem to encompass a specific kind of teenagers, so I can't really adress all those other questions.

Why is this even a question? It's "may contain content that is only suitable for a mature audience," not, "this content is mature." Completely different meanings and I have no idea why people struggle with that.

The rest of your post is mostly biased generalizations. And why are you worried that someone likes to play something serious or dark? Let people play what they want to play.

Gaming by itself isn't mature so no. Some games are just only suitable for a mature audience because of violence, sex, gore and other dark themes.

I think that mature games in modern day tend to refer to what's displayed on the screen, such as gore and violence like you suggested. But actual mature games can have more adult themes that apply to those who are older.

Let's look at Uncharted 4 for example. When Nate and Alayna (Elena? Idk how to spell it, sorry if I butchered it) argue over their trust of each other and how Nate went behind her back that speaks a lot to their marriage and to truly feel for the conflict I think it takes a more adult mindset, or at least someone who is older to really get the most out of that experience. 8-year old me might not have cared for it as much as 21-year old me.

So in a sense I'd say that yes, mature games can be 'mature.' However, the way you phrased your response made it seem like it was targeting more just the dark grittiness of games and how people's taste changes over time. I don't think a game needs to be blood-filled to be considered mature, and I think it is a massive problem in today's gaming landscape.

The general rule is people who play Rated M games because they're "mature" are not mature. You play games because they interest you, not because you fit in an age bracket.

Majority of the time, NO.

Just like in movies or TV shows. The only real thing that makes one thing mature rating or not is a certain level of violence, swearing or nudity.

If you want a true mature game, go play a game of chess.