Eventually, Aaron notices it first (Nothing can distract Temple from magic) and then asks if that is common.

"Ah, no... There was a bit of an accident during an experiment with the de-aging rune I found..."

"Wow. What did it do exactly? How long ago was that? Do you know if changed your lifespan?"

"I haven't dropped dead yet, which is a good sign! I feel as spry as I did when I was thirty. There's no good way to investigate the issue further. De-aging runes won't work on animals, and I won't risk someone else getting trapped in a child's form. Maybe with a few hundred thousand rupees' worth of equipment and staff I could figure out what went wrong... But as it is, I'm stuck like this."

"Uh, one can use sorcery to extend their lifespan, in theory indefinitely. But the result is the person being youthful twenty-something looking... There is probably some sort of analysis that can figure out the traits of this de-aging safely."

"Hmm, mm, I don't think we have the resources to safely investigate that... I'm certainly not going to use it on anything else..."

"I can drop the subject if you prefer to. But I wouldn't be surprised there is something to be done about it with sorcery."

"It's kind of embarrassing, that's all. If you have passive scans you want to try I can load it into the Guidance Stone..."

"It would be fairly easy to figure out how much youth you have and possibly if it's doing something unusual like not slowly erode away like normal youth does."

"Okay, we can take a look at least."

There is a direct contact lifeforce "touch", but that might be too risky... well, he figures a simple ritual that he can boost with his wakefulness and youth gifts.

So does Purah have a ton of youth? Or maybe he youth behaves differently?

...She's got a ton, and she's making more at a steady pace. Somehow.

Seriously? "Okay... I think we should be very careful of anything that involves you using any youth-fueled magic. Also, you generate youth."

"What the fuck?"

"Hmm, hmm... Now I want to figure out the de-aging rune even more... But Sheikah technology is scarily powerful. It can really mess you up if you're not sure what you're doing."

"I'm curious, but I want to... have several layers of protection and that might take some time to figure out. And my main concern is that it might still generate more while unattached from you and have some weird magical consequences."

"Our world is dealing with a magical city that is spreading like an infection. And that didn't require self-generating youth to get bad."

"Exactly what I mean. We woke up the Guardians and Divine Beasts, but then Ganon just used them against us! It made everything worse."

"What?"

"...Which part was a 'what'? Guardians and Divine Beasts, or Ganon and the Great Calamity?"

"The entire thing?"

"Well, back when Hyrule was still whole, because of all the prophecies of doom and stuff, the king had my sisters and I start excavating ancient technology and figuring out how to work it. We thought we were making great progress, too! But when Ganon finally did arrive... Everything we had worked to find and restore turned against us, turned evil, and helped destroy the land and spread monsters everywhere. It was massively bad."

"That is a way to put it, yeah."

"So messing with magic too carelessly, however fun, might be a bad idea."

"I wasn't planning to cause a disaster, but I understand being careful."