In his book Journey to the Center of the Earth, Jules Verne does not tell readers exactly how old the character of Axel Lidenbrock is. Axel is the naïve, cautious narrator of the book and the nephew of Professor Lidenbrock, the man who discovers the map that leads to the center of the earth.

Although Axel never specifies his exact age, readers can infer that he is a young adult who is either in his late teenage years or early twenties. One main clue that this is his age is that he is engaged to the professor's seventeen-year-old goddaughter, Grauben. His infatuation with her is characteristic of a young person in love for the first time. Recall how he says,

Gräuben was a lovely blue–eyed blonde, rather given to gravity and seriousness; but that did not prevent her from loving me very sincerely. As for me, I adored her, if there is such a word in the German language. Thus it happened that the picture of my pretty Virlandaise threw me in a moment out of the world of realities into that of memory and fancy.

Axel's intense love for Grauben and his eagerness to marry her as soon as possible suggest that the couple is planning to start their adult life together. Initially, Axel does not want to go with his uncle because he would rather stay with Grauben, but she encourages him to go on the adventure. While he is on the journey, he grows a great deal, developing from a hesitant, skeptical boy who is often annoyed with his uncle to a mature man. This is evident when he says,

I was now the nephew of a great man—which is not a privilege to be despised.

In a way, Journey to the Center of the Earth is a coming-of-age story for Axel, as he learns a great deal about being strong, brave, and supportive.