There are no more potential-killing words of creative advice than “write what you know.” Certainly it’s a shame that when donning her screenwriter chapeau, Valeria Bruni Tedeschi — a fine actress and a director with a deft, light touch, especially with breezy character comedy — seems to have taken them so to heart. Once again she goes back to the autobiographical well for her latest directorial trifle, “Forever Young,” which she co-writes alongside Agnès De Sacy and regular collaborator Noémie Lvovsky.

Once again the result is set in a rarefied world of which Bruni Tedeschi has intimate knowledge: this time the 1980s acting school run by the late French theater, opera and film director Patrice Chéreau. And once again she fails to make much of a case for why any of it should resonate with anyone outside this tiny, hermetically enclosed community. Staying in your lane is hardly a virtue when your lane is more of a gated gravel driveway leading to a faraway secluded villa, possibly surrounded by a moat.

The film opens in the tousled, flushed, keyed-up register in which it will continue for more than two long hours, abetted by Julien Poupard’s pretty but soapily saturated, insistently close-up camerawork. Bruni Tedeschi’s presumed avatar Stella (Nadia Tereszkiewicz, limpid of eye, luscious of pout) is writhing around on the floor in the throes of simulated passion. She is auditioning for a coveted spot in Chéreau’s Theatre des Amandiers, though the volatile director, here played by the volatile Louis Garrel, is not present. Instead Stella is ripping her figurative heart — and literal breasts — out in front of a largely stonefaced panel led by Chéreau’s right-hand-man Pierre Romans (Micha Lescot).

Convinced the audition was, in more ways than one, a bust, Stella barrels into the bathroom as tears begin to carve mascara channels down her cheeks, and meets fellow applicant Adèle (a welcome but underused Clara Bretheau), an earthy redhead with Natasha Lyonne hair and no underwear. They bond instantly, and so it is with much rejoicing and youthful exuberance — so very, very much youthful exuberance — they greet the news that both have been selected. Among the others joining this little thespian elite are: pregnant but determined Camille (Alexia Chardard); Franck (Noham Edje), who’s expecting a child with his young wife, though that doesn’t stop him sleeping around; Juliette (Liv Henneguier), who develops an unhealthy fixation on Pierre; and moody, broody Étienne (Sofiane Bennacer), a drug addicted Brando-alike from a troubled background. (He even gets to holler “Stella!” at one point.) Étienne threatens to throw himself off a balcony if Stella does not sleep with him. She does. They get involved with each other, which is no mean feat for people as self-involved as they.

There are genuinely dramatic interludes here that could have contributed to a much better film. An AIDS scare rips through the class, who have all been youthfully, exuberantly sleeping with one another. Pierre is introduced to heroin by Etienne; Chéreau is shown snorting fat lines of cocaine. Suzanne Lindon plays one of the year’s rejects, whose wheedling, obsessive background presence — when she takes a job in the school’s cafe just to be near the action — is a squandered opportunity for actual conflict. Most strangely of all, for a film that states and restates the bone-deep vocational importance of the acting process, there is little real sense of the euphoria of performance, or the irresistible lure that the stage exerts on these kids. Even the potential to have the play-within-the-film (here Chekhov’s little-known “Platanov”) somehow comment on the characters’ lives, as in last year’s “Drive My Car,” goes largely unmined.

Instead, especially in the final stretch, as Étienne slides deeper into addiction and Stella becomes more anxious for him and fearful of his jealousy, the film starts most to resemble another ’80s-set work of fictionalized autobiography by a female filmmaker examining her own creative coming of age: Joanna Hogg’s “The Souvenir.” It’s a comparison that does Bruni Tedeschi’s movie no favors, especially in one key regard. Where Hogg gives a clear-eyed, sometimes painfully self-critical perspective on her background of privilege and comfort, “Forever Young” seems to exist partially to remind us that enjoying elite social status is nobody’s fault, as if wealth is a helpless condition that it’s futile, and rather gauche, to mention. In marked contrast to hard-up classmates dependent on the school’s sponsorship, Stella lives in a large house and is waited on by a butler. But when Étienne makes a glancing allusion to her family’s money, she immediately looks stricken. “Why would you ask me a thing like that?” she reproaches. The exchange is proffered as an example of Etienne’s cruelty toward her, and the issue is simply dropped.

Suppressing a smirk as Stella rips open her blouse at that first audition, Pierre asks her, “Do you think an actress has to be an exhibitionist?” A trembling, teary silence ensues. But while getting physically naked is obviously not a prerequisite for becoming a great actress, the ability to metaphorically bare yourself (and subsequently bear yourself) is maybe the key requirement for anyone wishing to create profound art from lived experience. Here, just as Bruni Tedeschi’s last Cannes competition title, “A Castle in Italy,” pivoted on the highly relatable plight of being forced to sell the family Bruegel, there is a strange, self-pitying myopia around the wealth and privilege to which Stella has access, as though she is to be excused any interrogation of those advantages because of how well-meaning and guileless she is. Long before the end of this indulgent, histrionic personal history, we’ve lost patience with this exposed-nerve character, for whom every feeling is deeper, rawer and more passionate than normal — except the feeling that she might ever be in the wrong.