Yes, technically Marco is much older than Star, but his mentality seems to change along with his body depending on which dimension he's in. Which makes sense, as the brain does continue to grow until your twenties, so when he becomes 14 again, his brain is once more undeveloped.

Marco retains all of his Neverzone memories and skills regardless of which dimension he's in. That means he's mentally 30 and remains so no matter where he is.

Yeah that's something to think about Hawas1983.

No, not really. You can have a lower maturity while retaining memories. Heck, we see that IRL. Marco may have his adulthood memories, but when he returns to being a teenager, he mentally becomes one too. Heck, we actually saw that happen. But when he goes and becomes an adult again, his maturity returns.

That's not how brains and minds work.

Marco spent the better part of 16 years living as an adult. He acquired new knowledge like learning ancient languages and new skills like swordsmanship and riding a dragoncycle. Acquiring new knowledge and skills physically changes the brain. New dendritic connections are formed. That doesn't just go away when Marco reverts to his teenage self. If it did Marco would be sustaining massive brain damage as those tissues disappeared from his brain. However we know those tissues didn't disappear because Marco states that he remembers everything that happened to him in the Neverzone and he still has full command of the skills he acquired there. Marco retains his adult brain even in his teen body.

Not only did Marco's brain change, his mind changed as well. Marco thinks like an adult. He had to if he was to survive. Marco spent 16 years exercising adult reasoning, adult judgement and adult perspective. After that Marco can no more go back to thinking like a teenager than any of us can go back to thinking like an infant. Those of us who are adults know the changes that transition makes in you and that you can't go back to the innocence of childhood. Marco has simply seen, learned and done too much to ever be a child again.

Running with Scissors was just supposed to give Marco a power up for his adventures in Mewni and to replace the dimensional scissors so he and Star can continue traveling dimensions. The problem is they did it in a way that ended up having massive implications for Marco and everyone his life touches. Marco should be a totally different character. He's an adult in a child's body. How many stories have played with that idea? The writers couldn't live with the idea of an adult Marco hanging around with teens so they initially blew the whole thing off by claiming Marco remembers nothing about his adventures in the Neverzone. Then they have him announcing that he remembers everything about his adventures in the Neverzone and using the skills he acquired there outside of the Neverzone.

Children aren't going to make a big deal of it because Marco still looks like a child so to them he is a child. Adults are going to see this much differently because we know from direct experience what it means to become an adult and that once you've crossed that threshold there is no turning back.

Ok thanks for sharing these details.

I've had this discussion before.

@Hawas1983

You can try and argue that point all you want, but the fact of the matter is that despite retaining his memories, we saw for a fact that he has the mentality of a 14/15 year old again when he de-ages, and regains his adult mentality when he ages up again. This shows the regression of his mind when he hops time dimensions.

Look at it this way, there are plenty of stories that have characters who are reincarnations of someone who later regain their memories of their past lives (this is a fairly common anime trope when dealing with reincarnated characters), yet they still maintain the maturity and mentality of the age they're currently at. Or look at characters that stop aging at a certain point, like vampires for instance that are turned when they';re kids and so remain kids., They can live for hundreds of years, but still retain their child mentality, because they haven't grown and developed.

It's more or less the same with Marco. Yes, he lived for several decades and grew into an adult, but when he grows down again, his development reverts to that age as well, because in THAT form he hasn't developed. Sure, there may be some differences personality-wise that are a result of his experiences, but mental-wise, he's a teenager again. This is shown in his behavior, mannerism, and thought process.

What we've seen is that the writers are trying to play the implications of Running with Scissors both ways. You are free to interpret that episode in any way you require to maintain the fantasy that Marco can slip back and forth between 15 and 30 but the show itself maintains that Marco retains his adult mind.

You cannot maintain that Marco can simultaneously maintain the memories and skills he acquired in the Neverzone while remaining at the maturity level of a 15 year old when he reverts to his teen body. Human psychology simply doesn't work that way. That you don't understand that renders your point moot. It simply doesn't square with the realities of human psychology. Marco can remember all of it or none of it. He cannot selectively forget the parts that you or the writers find problematic.

Marco's mind has been profoundly changed by his experience. His way of thinking is that of an adult because he remembers thinking like an adult. It's the only way he thought for the better part of 16 years. Your argument presumes that Marco can selectively forget certain parts of his experience while retaining the memory of others. On what do you even base that idea? How would it even work? If Marco remembers how to use a sword how would he forget the thought processes and responsibilities involved in fighting with a sword? To effectively use a sword you have to think like a swordsman and Marco thinks like a swordsman when using his blade as he is effective with it even outside the Neverzone.

Marco's behavior post-Neverzone is the result of the writers trying desperately to ignore the implications of Marco being a 30 year old man in a teen body spending his time with other teens. They basically swept the problematic aspects of Marco's experience under the rug while pulling out the convenient bits like skills and memories whenever they benefit the plot. The writers made a bad decision with Running with Scissors when they decided to ignore the monster they had created. They are trying to have their cake and eat it, too, and you are OK with that. I have an adult understanding of the world and what it means to be an adult. Marco can't selectively remember how to use a sword while forgetting all of the implications involved with using a lethal weapon against living opponents. That is simply not psychologically possible. I fault the writers with not taking that basic fact of human psychology into consideration when they crafted this episode.

Marco was 15 years old right before he entered the Neverzone where he aged 16 years so

Physically is he 15 years old

Mentally is he 31 years old

However after that it is kind of unknown to me as he went into the Neverzone a couple of times again for an unspecified amount of time so at the end of the series do I think that Marco is

Physically about 16 years old but

Mentally about 32-40 years old as I think that the entire series plays out for about 2 years with Marco starting at 14 and being about 16 at the end and Star being 15 and being about almost 17 at the end