The problem with a bildungsroman is that the protagonist eventually grows up.
There are several interesting entries on About Last Night about David Copperfield, about the brilliant beginning, of Copperfield's sad and poetic early childhood, and the inevitably more mundane life he leads afterward, for all its Uriah Heeps and Mr. Micawbers. I recently reread it, and though I would not have put the boundary down as sharply as Carrie Frye (CAAF) and Graham Greene do, but there is a lot of activity in the book, including a weird doubling of fallen women, elaborate scheming, and shipwrecks.
Such depictions of childhood have a unity that the adult world lacks, and the potentialities of that time can never fully be realized. I am put in mind of a book from my own genre, SF, called Emphyrio by Jack Vance. After a somewhat melodramatic preface, it depicts the odd and somewhat ominous childhood of a boy named Ghyl Tarvok (Vance's made-up names always have a specific rhythm to them) in a city called Ambroy. He is raised by his mysterious father, Amiante, a brilliant craftsman in a world where mechanical reproduction is banned.
The first part of the book has a tender and melancholy mood that is rare and hard to maintain. There are mysteries to the half-ruined city, and Ghyl, amid all the activities of his youth, tries to puzzle them out. Then, in the latter part of the book, he goes offworld, has adventures, finds some things out...none of it has the sombre energy of the first part.
But such complaints just show how demanding we are when a writer raises our expectations. Dangerous, to be too good at the beginning of a book. Make your protagonist's childhood mundane and somewhat tedious, and we will find his young adulthood much more interesting....