I really dont understand why

I mean the mc probably would have never been kept and raised by another minor. Like wasnt he 10 and the groomer brother 20, if it was a slightly more acceptable (4-5 years or less) then the brothers wouldn't be able to own property to hide mc.

But he wasn’t hiding him ? he just took him in. If they were closer in age he still could’ve looked after MC. They also would’ve let them stay together since he was the only guide compatible to him. It would’ve taken out the aspect of him being a groomer and made him a childhood savior/ friend instead.

This dude went and took a child and kept him, with the usual government response suppose to put them into a foster center for other children who are alone due to gates. If the groomer wasn't an adult he wouldn't have the ability to ensure the mc gets stuck at the esper center and raised in his own private home. MC would have been stuck as a personal guide yes,but probably raised beyond the groomer's personal toy and he'll probably would have gotten more than 3 outfits or an actual socialized education by the time it matches the story. A powerful child esper would have less influence than the adult version, like other espers, guides, and staff of the area never mentions how werid he was raised there and never leaves. Hell the non groomer brother would have known the existence of mc cause the groomer brother wouldn't have been able to influence the executives to him mc that well at age 15, they would have to share from an early age especially as one of them needs guidance way more.
In the end it would have been a childhood friend story where the mc would have more freedom since his legal guardian would have been some executive that wasn't the brothers, or at the next option he would be become a ward of their parents and he's stuck under the same roof and still shared between them.

I mean but this is going off the story exactly as it is. Im saying they could’ve written it with a smaller age gap and still written it to be the same plot. The details would’ve changed but the overall story wouldn’t have to be changed drastically and then we wouldn’t have this groomer plot