In the history of Marvel Comics, fans can notice a tendency to keep its younger characters from growing up, keeping them teenagers or kids for years, even decades. Part of this has to do with Marvel’s sliding timescale, which ensures its characters only experience ten years of history regardless of how much time passes in the real world.

Because of this, early Marvel characters like Spider-Man and the Human Torch aged from teenagers to early adulthood, but characters introduced more recently remain perpetually young. But more recently, many characters who were kids for years are finally getting a chance to experience adulthood. This trend is also happening in the Marvel Cinematic Universe, where younger superheroes are preparing to take the stage in MCU Phase 4, both in films and Disney+ series.

Let’s take a closer look at some of these more popular characters, see what led to their sudden increase in maturity, and speculate on what this means for their future in the MCU.

The X-Men’s Eternal Teenager, Kitty Pryde

Introduced in Uncanny X-Men #129 (1980), Katherine “Kitty” Pryde was a thirteen-and-a-half year old girl who learned she had the mutant ability to phase and walk through solid objects. Filling the role of a “kid sister” to older characters like Storm and Wolverine, Kitty was actually allowed to age as she trained with the X-Men, growing into a fifteen-and-a-half year old by the mid-1980s. Once Kitty turned sixteen, however, her aging stopped. With writers and artists joking that Kitty had celebrated more sweet sixteen birthdays than any other comic book character. This was largely to keep Kitty a relatable figure for younger readers who enjoyed watching her grow up (but never quite reach maturity).

Eventually, however, Kitty’s age became an issue thanks to her attraction to older men. Upon joining the X-Men, Kitty gained an immediate crush on her teammate Piotr Rasputin (aka Colossus) who was likely in his early twenties. While that relationship was basically chaste, Kitty later became romantically involved with worldly secret agent Pete Wisdom when she joined the superhero team Excalibur. To keep these stories from raising uncomfortable questions, Kitty was finally allowed to grow up – attending college (and tending bar) in one comic book storyline and eventually rejoining the X-Men as a teacher and eventually leader.

Today, Kitty is likely in her mid-twenties and her stories emphasize her maturity – by having Kitty get engaged to Colossus and serving as headmistress to one of the X-Men’s schools. Kitty’s rebellious teenage self still gets featured in the comics, however, through stories set in the past (such as the Wolverine: First Class series) and alternate versions of herself (such as her Ultimate Universe counterpart who fell in love with the teenage Peter Parker).

Power Pack, Marvel’s Youngest Superhero Team

In 1984, Marvel created its first team of preteen superheroes with Power Pack, a comic about four siblings – Alex, Julie, Jack, and Katie Power – who received fantastic powers from a dying alien. As this was the Marvel Universe, the kids found themselves involved in some very dark events – including the Mutant Massacre (where underground mutant communities found themselves being hunted by mutant-hating Marauders). Other storylines dealt with social issues such as drug abuse, runaways, bullying, and homelessness. Nevertheless, the kids remained optimistic and excited by the idea of being superheroes – especially since this meant they got to team-up regularly with the X-Men and Spider-Man.

Since Power Pack’s primary appeal was to see the Marvel Universe through the eyes of a child, the kids barely aged at all during the comic’s 62-issue run. Even when some of the children guest starred years later in other comic books, they only seemed to age a few years, if at all. In 2005, however, Power Pack was relaunched as several miniseries, each teaming the preteens with a new superhero, which took place in a separate continuity from the mainstream Marvel Universe.

Due to the lack of attention the original Power Pack received, two of its members – 11-year-old leader Alex (Zero-G) and 10-year-old Julie (Lightspeed) – finally grew up when they reappeared in Fantastic Four and Runaways. Alex became a college-age young man (and professor to a new team of young geniuses in Future Foundation). Julie, meanwhile, pursued an acting career, attended college, and came out as bisexual. The other two members, 8-year-old Jack (Mass Master) and 5-year-old Katie (Energizer) have not been featured as much – although Katie recently appeared in Power Pack #63 as a middle schooler.

The Fantastic Four’s Franklin and Valeria Richards

The son of Mr. Fantastic and the Invisible Woman, Franklin Richards likely has the longest childhood of any character in the Marvel Universe. Born in 1968 in Fantastic Four Annual #6, Franklin managed to grow to early childhood – and then stayed an early preteen for almost fifty years. Some stories did show Franklin (an Omega level mutant) temporarily aging himself to adulthood or being replaced by an alternate future version of himself. Sooner or later, however, the status quo would reassert itself and Franklin would regress to a grade schooler.

Things were even weirder for Franklin’s sister, Valeria. Originally a stillborn child of Reed and Sue’s, Valeria would return years later from an alternate future as an adult to aid her family. During the adventure, she regressed back into her mother’s womb and was born again, becoming Franklin’s younger sister and eventually manifesting her father’s genius-level intellect. While she eventually aged three years (with Franklin staying roughly his same age), Marvel’s sliding time scale seemed to indicate she would stay a pre-adolescent like Franklin, too.

In the aftermath of Marvel’s 2015 Secret Wars event, however, both Franklin and Valeria spent years outside of normal continuity rebuilding the multiverse. When they returned in the new Fantastic Four comic book, both had become teenagers, with Franklin taking on the codename Powerhouse and Valeria calling herself Brainstorm.

Ant-Man’s Daughter Cassie Lang

In Avengers: Endgame, Scott Lang (aka Ant-Man) emerges from the Quantum Realm only to find that five years have gone by, and his ten-year-old daughter Cassie is now a teenager. Fortunately, in the comics, Scott didn’t have to be absent for all of those years as Cassie is one of the few kid characters to grow normally (by comic book standards). Appearing first as a young child with a heart condition (which motivated Scott to steal the Ant-Man suit and save the doctor who could cure her), Cassie appeared intermittently in guest appearances – initially as a preteen until she suddenly appeared in her teens with the ability to grow to giant size and became the hero Stature in Young Avengers.

Cassie also grew up in the alternate future depicted in Marvel’s MC2 imprint (which also featured “Mayday” Parker (aka Spider-Girl), the teenage daughter of Spider-Man. In this universe, she took on the identity of the shrinking hero Stinger, a name her mainstream counterpart has also adopted (and one the MCU Cassie may also take on in Ant-Man 3). Much like her MCU version, Cassie did most of her growing up offscreen, making it easier for comic book creators to not lock her in at a certain age.

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This trend of allowing young heroes to age up may continue in future MCU movies, as mainstays like Iron Man or Captain America move on, leaving open spaces for new heroes to carry on in their place. Considering how the MCU has influenced depictions of comic book heroes, this may carry over to Marvel Comics as well, as more heroes who have enjoyed a perpetual childhood finally get a chance to explore stories about their teenage years and adulthood.

Next: MCU Phase 4 Theory: Endgame’s Iron Man 3 Cameo Sets Up Young Avengers