On Rudeus' age I'm in the camp,he became a child but because he had his past adult memories - he resembles those abnormal gifted children who find it easier to talk to adults than kids their own age. Those kids have brains that work differently. BTW Rudeus keeps calling himself an "adult" throughout his second childhood until **spoiler moment** he finally admits that "he was just a child pretending to be an adult because of his past memories." He's incredibly mature when he becomes an adult again. Although I'll concede it's a difficult philosophical question asking HOW OLD ARE YOU? if you reincarnated as a baby but retained all your memories. As Mushoku has showed on one hand, you'd learn faster and optimise mental growth taking advantage of your youthful brain. However to the world, you'd be a child and treated as such until you grow up again.

Rudeus is an amazingly well written character and the perfect protagonist for Mushoku Tensei 👌🏽

I think most people forget the mechanics and implications of reincarnation. Which is your previous you is dead, and you are a new person, even if you have memories from before. Even Rudeus himself falls in that error and has trouble disassociating himself from his previous self. A nice choice by the author really. It takes Rudeus a long time to finally admit having memories from a previous life doesn't really make him an adult (plus a lot of his experiences are meaningless in his new environment). I think you'd experience the same if you were reborn 50 to 100 years after your dead. The world, society and its rules would have changed considerably and you'd have to relearn a lot of it.

Rudeus is not a mary sue character , He has flaws but those flaws makes him a good character

I love Rudeus Greyrod.

No memories of your past are going to save you from the effects of a changing brain and the hormones from puberty, and I think the author had something similar in mind while writing Mushoku Tensei. If you've read the light novel, you'll likely notice that Rudeus' behavior is appropriately childish and immature during his childhood and teen years (even in his thoughts). But he becomes appropriately more mature once he leaves puberty behind. He still makes jokes from time to time but you can feel the difference.

Honestly he have all the traits of a character I hate. I admit his action r wrong and some push my boundaries. But I still like him as a character and that said a lot abt character writing in mt