~ The Ashen Herald ~
I'm so glad he was aged up. It's a very profound, bittersweet and badass moment. A true sacrifice unless Bonney undoes it lol.

But since Hiyori had to live out those 20 years, I think he'll stay aged up and let his mind mature and catch up ASAP and he's technically older then her so its better this way too.

It's a similar storyline to Ocarina of Time. Boy sacrifices youth to become a man and necessary hero.
That‘s true, OoT had a similar thing. Adult Gon in HxH is like that, too. I think it was a beautiful thing and it also helps him defend Wano in the future when he opens the borders for good.