It’s a 4 month old post, so I assume your brother has already watched Attack on Titan but I’ll answer anyway:

I recommend he follows the 3 episode rule. 5 minutes isn’t even enough to judge the anime. If he doesn’t want to watch it at all, you have two options. Option 1: It’s literally his life, therefore his choice. Let him do as he likes. If he doesn’t wanna watch it, don’t force him to. Option 2: Give him some spoilers which will get him interested in watching it. (I have tried this method on many of my friends to get them interested in anime that I suggested)