Translations for youthful in French

Here are paragraphs from public domain books translated:

"I wonder whether you could get on friendly—or at least on talking terms with the fellow," he said, at last. "You seem to have a sort of genius for establishing relations with people—seempathy, I suppose, or animal magnetism, or youthful vitality, or something. I am conscious of it myself."	— La question, dit-il enfin, c’est de savoir si vous pourriez vous entendre – ou même simplement causer – avec notre homme. Mais vous semblez avoir une sorte de génie pour vous imposer aux gens : don de sympathie, pouvoir magnétique, effet de vitalité juvénile, ou quelque chose d’analogue, je suppose. J’en ai, pour ma part, le sentiment très net.
The Lost World, by Arthur Conan Doyle	Le Monde perdu, de Arthur Conan Doyle

Such was the story of his arrest as narrated to me by Arsene Lupin himself. The various incidents, which I shall record in writing at a later day, have established between us certain ties....shall I say of friendship? Yes, I venture to believe that Arsene Lupin honors me with his friendship, and that it is through friendship that he occasionally calls on me, and brings, into the silence of my library, his youthful exuberance of spirits, the contagion of his enthusiasm, and the mirth of a man for whom destiny has naught but favors and smiles.

C’est ainsi qu’un soir d’hiver, Arsène Lupin me raconta l’histoire de son arrestation. Le hasard d’incidents dont j’écrirai quelque jour le récit avait noué entre nous des liens… dirai-je d’amitié ? Oui, j’ose croire qu’Arsène Lupin m’honore de quelque amitié, et que c’est par amitié qu’il arrive parfois chez moi à l’improviste, apportant, dans le silence de mon cabinet de travail, sa gaieté juvénile, le rayonnement de sa vie ardente, sa belle humeur d’homme pour qui la destinée n’a que faveurs et sourires.

The Extraordinary Adventures of Arsene Lupin, Gentleman Burglar, by Maurice Leblanc

Arsène Lupin gentleman-cambrioleur, de Maurice Leblanc