Just my multishipper brain talking.
Often, Tegan is friendly with Nyssa to the point that they could be considered a couple or that the narration called them a couple in farewell Sarah Jane, but Nyssa seems teenaged/underage at times. She’s often written with a somewhat flowery/clunky Shakespearean language, and initially she was just a satellite character daughter of Hellas (the character who eventually was split into Tremas, Seron, Neman, and Luvic) so. I’ve seen people thinking even Jamie is 17. So yeah, there is a supposition that Nyssa might be considered underage or at least a bit young. Some say her age is the season number. Basically she’s born in 1963.
It all started with “the Keeper of Traken”, honestly. It originally only introduced four Trakenites. The old Keeper, Hellas, Zorca (a male character that became Kassia and Katura), and Nyssa.
Hellas was the leader of the scientific grays, who became the fosters, and Zorca leader of the zealous/religious blacks, who became the consuls and were evoking a demon called Mogen. And it was supposed to be a medieval monastery. Mogen then turned out to be an old enemy of the Doctor who became the last of his kind. Possibly due to an adventure where the doctor was there too.
Apparently Hellas and Zorca would propably have been vaguely middle aged and Nyssa vaguely young.
Then it got changed to resemble Meglos less, and became Shakespearean medieval Art nouveau.
In the actual tKoT that aired, it seems like that Nyssa and Luvic are an younger generation than the rest of the characters, being styled and somewhat written as “the kids of the bunch” or at least slightly more immature than the old Keeper, Tremas, Seron, Kassia, and Neman. Yet being apparently still adults, Nyssa still invents a stun gun and Luvic gets to become a consul/keeper.
More specifically, flashback Kassia is the same age as Nyssa was in tKoT, they’re both 18. Luvic is propably a bit older. Maybe 30 or something. For a while I thought he was 23 because of a character.ai thing.
Anyways tKoT takes a lot from Shakespeare. In Shakespearean plays, the same actor plays the same character in the same play, but throughtout the actors life, based more on vibes. Like Hamlet, who is canonically 30 in the play, yet is somewhat “teen coded” so an actor who plays Hamlet would start playing hamlet when he’s 13.
So, maybe I should take the actor ages as a grain of salt and now how old the characters actually look, we know Kassia didn’t actually have painted eyelids, it’s just a theatre makeup look, so likely she didn’t actually look in her mid-to-late-20s at 18 and then kept on looking mid-to-late-20s at 40. It’s just ability over appearance and Sheila Ruskin is just good at theatrical acting and was a 35 year old who looked mid-to-late-20s. (Kassia, Seron, and Katura were all going to be played by other people at one point) But I like to think maybe the master did slip some of that tiger emerald from that one audio to her.
Basically I don’t think you’re really meant to notice the actor ages and looks, you’re meant more to watch stuff fast enough to not really notice anything.
And the fireworks from the wedding weren’t actually still. But maybe those skies that don’t quite look outdoors are just how Traken looks.
I thought Nyssa and possibly even Luvic are meant to be that kind of “teen coded adult” that hamlet is.
Heck, I can be considered a teen coded adult, since I’m not completely independent yet and I still give off vibes of being in high school. I need to grow! To have less weird thoughts about fictional characters, and realize it’s just fiction!
And despite being teen coded, Luvic gets stuck on a chair for 1000 years that turn out to be four weeks, and Nyssa looks exactly the same (even in age) to the more clearly adult Ann Talbot. Not only that, but Nyssa leaves to get a job!