Antonio "Tony" Márez narrates the novel, telling the story of his early youth. Luckily for us, the story he tells is a good one. Antonio's childhood was filled with magic, murder, mysticism, and lot of other cool things that don't necessarily start with the letter M.
While the reader doesn't know exactly how old Antonio is as he narrates, it's clear that he's reached a point where he can look back objectively at times, but he can also romanticize his younger years, like when he says, "Time stood still, and it shared with me all that had been, and all that was to come…" (1.10-12) Cheesy? Yes, but Antonio pulls it off.
And hey, romanticizing is something we all do. Maybe that shot you took in your fifth grade basketball game wasn't actually from half-court, but that's the way you're going to tell it, and that's okay. It's believable in this case because Antonio the narrator has full access to the thoughts of his younger self. He even has the ability to recall specific dreams he had in great detail, which seems almost like a superpower. After all a lot of people can't remember what they dreamed last night let alone what they dreamed when they were in first grade.
While there is a bit of the romantic in the narrator, he does seem to be trustworthy. His knowledge and crazy ability to recreate the time of his youth match well with Antonio's younger self's skills of observation. Of course, he is telling his own story, so questions of trust can still crop up. Yet Anaya never gives reason for the reader to think that Antonio is lying as he recounts the past, so we can't help but take him at his word.