Wow... this is some sleeper gourmet. It's pretty common for manga to put emphasis on the word "youth" as a core theme, but it's rare for it to be both unspoken, and also actually felt. Often it just feels a bit hollow, like an imitation of what youth could be.
Another commenter said they're glad this is a oneshot, I have to agree. This emotion is powerful but, it would be lost completely in a serialization.