Being forever young is nice, but the MC looks too young to comfort never aging. I have seen baba lolis several times, the other side of a coin, well, it's right now in the making.
I hope that he would not be a dense idiot who doesn't recognize his strength compared to world normal sense. But it's kind of his grandpa's fault, he never shown him how outside world works. Yeah just toss him outside his comfort not explaining anything more than about supplies and where the next city is located... Great parenting. /s