I came back to reread it cuz it's peak and think of it like this, the forest is magical obviously there's literally unicorns, fairies, a werewolf and other sh8t, so obviously we can assume that this would also slow down a humans aging, I think Tarou lived 100 years because the forest slowed down his aging process, from what Tarou looks like I guess he's at most a teen living with Uru those 100 years, came to the human world and aged normally again cuz he isn't in the forest anymore and came back as an adult.
As for Tarou's maturity, with the way Uru treats him and the forest taking care of him basically he'd have a maturity of that of a human whose been kept in a very secure and no danger environment where their pampered all day long, he has nature skills but his mindset is that of a teenage boy, he's curious and strong willed, a personality of someone who doesn't fear danger because he knows nothing will happen to him.
Overall even if Tarou is like that, he expresses what he wants and is very secure in his decisions and it's not as weird as long as they did it when Tarou wasn't a minor which I would assume since he's been in the human world for long I would assume he aged normally now that he infact is an adult
Obviously his age really is a confusion, in one hand he lived for 100 years meaning he technically IS 100 years old by the definition of age, but we also gotta factor in that it's highly possible the forest slowed down his human aging since we do see him grow up while with Uru. Technically he is 100 yrs old but his true age assuming his age was slowed would be that of a teenager before Uru gave him back to the human world
This is a weird one for me. It's defined cute and wholesome, and, I'm not exactly against the raise-your-lover trope – it is something highly dependent on the execution for me. In this case, I think they establish clear enough boundaries on Tarou not feeling a fatherly figure in Uru for their relationship to not feel weird for me – but I think we needed to see more of Uru's thoughts, too.
Here, the weirdest part for me is this "Tarou was over 100 years" but because it just leaves too many questions for me about where to stand on his maturity... like, sure, he's 100% an adult by the end of the manga, but I'm just left wondering just how old Uru would supposedly be (in relation to hi maturity, and not literal years) or if that's even applicable to him as well. *Is* Tarou even subject to this scrutiny, too? As in, is he even human?? Is the 100+ years a *him* thing, or a *being inside the forest* thing?
I like this story, in a way, but I'm also left wondering about one too many things for me to consider it in any higher regard.
If only the author wasn't into tiny twinks... sigh......