Well, I agree that "mental age" is not a real measure, and adding two lifetimes together makes no sense.
But one thing: Rudeus carries decades of memories from his past life, which takes him far from being a normal child.
People often point out the parts such as: non-consensual touching, or the sexualisation of child characters.
I think flawed main characters are fine. They too carry the potential to be great, and inspiring in so many ways, and Rudeus does exactly that!!
But my objection is very specific: It's how the story looks at a flaw.
The story often likes to portray the flaws as a joke. A little comedy is okay for most things, but not for the most sensitive ones.
Touching someone without their consent, especially when children are involved, goes beyond discomfort when it's shown through a comedic lens.
And this matters even more for Rudeus, because he carries his adult memories, flawed as they may be.
And it's not that the story doesn't know how to show proper care. It did it beautifully for Paul and Rudeus, in so many ways.
I hoped it would do better at some point, but it never really gives personal boundaries the same care.
Almost everything else in Mushoku Tensei is really good ✨
I'll never understand people claiming Rudeus has a mental age of 40+ simply because he has memories of his past life. What actually determines someone's mental maturity? Isn't it influenced by brain development and life experiences? So what exactly makes Rudeus mentally 40+?
First of all, he was reincarnated into a new body with a developing brain. Secondly, he spent years of his previous life as a shut-in, isolating himself from society and remaining confined to the same environment. This contributed to his psychological and social stagnation, making him emotionally and psychologically stunted
You can't simply add together all the years he's lived and call that his mental age. Even in real life, people of the same age can have vastly different levels of psychological maturity let alone someone who's been reincarnated into a completely new body with a developing brain