The Sin of Youth by Matheus Mundim
The Sin of Youth is about getting old and the desire to go back in time to change things, relive moments, and flames.
The Sin of Youth is a contemporary novel with philosophical existentialist characteristics.
The book portrays a moment in the life of young Jamie in which he wakes up in a room in another world. As he leaves the room, he sees a group of people and notes that they are all the folks he once knew and loved in his life, all together and gathered, drinking and partying. 
Impressed and extremely happy he approaches, confronting Thomas and Luke. They explain that the party was to honor the farewell of his youth. It was the last moment to hang out with everybody and say goodbye.
Sad and frustrated, he asks what he can do. They then tell him about the Elder Wizard, who would own the time, and could help him maintain his youth. However, they warn: the way to reach the old man is difficult and tortuous, few have succeeded, and, mainly, time is short.
Still, Jamie insists, following a path that makes him come across old memories, old loves, old "I's", wondering what his past "selves" would do if they knew the unfolding of such pure and delicate scenes. If they only knew how some words would mean after a few years.
It is a mix of pain, sensitivity, frustration, and happiness to review some moments.