When HBO announced last month that Girls would end after its sixth season, that seemed about right. Some TV shows are built to run forever, because they have a premise and/or characters who transcend the particular moment in their story in which the show began. Louie (a show that was a big influence on Girls) is on an indefinite hiatus, but is an elastic enough idea that the head of FX recently suggested Louis C.K. could return to it periodically in his 50s, 60s, and 70s. Rumors persist that NBC will revive the original Law & Order at some point, and Sam Waterston has at least another decade of self-righteous reactions in him.

Girls, though, is about a very specific time in the lives of its four title characters, and about telling their stories in a very specific — and, always, polarizing — way. Lena Dunham and company have presented the early-mid 20s of Hannah and her friends not as the carefree adventure that's usually depicted in fiction about people this age, but as a disorienting, oppressive horror show. They want to do everything, but for the most part lack the skills, the wisdom, and the resources to do much of anything. A time of allegedly limitless opportunity instead turns into an endless opportunity to fail in humiliating fashion.

The show presents those humiliations with such artistry that they're often poignant, or hilarious, or both at the same time, but there's always been a ticking clock on how long it can linger in this period. At a certain point, the girls either have to start growing up, which fundamentally alters the subject and tone of the show, or the repetitions of their failures become tough to endure even for those of us who haven't already dismissed it as the worst thing Western civilization has produced since the Hot Pocket.

Some of that strain is already apparent in the start of season 5, which debuts Sunday at 10 on HBO. The girls are, if not growing up, then at least trying out the customs of those who do. The season premiere is set on the day of the wedding between the narcissistic Marnie (Allison Williams) and her even more self-involved musician boyfriend Desi (Ebon Moss-Bachrach). Hannah (Dunham) is many months into a mostly healthy relationship with the exceedingly normal Fran (Jake Lacy). Shoshanna (Zosia Mamet) has grown accustomed to her new job and life in Japan. Adam (Adam Driver) is enjoying steady acting work, and he and Jessa (Jemima Kirke) are both doing well with their sobriety.

As Jessa puts it, summing up not only her own goals, but where all the characters seem to be at at this stage of the series, "I'm done being shitty. Shitty is old news."

Saying that and being that are two different things, of course, and Girls continues to mine comedy out of the vast gulf between its characters' aspirations and their reality. Hannah, for instance, is still a constant source of exasperation for the principal at the private school where she teaches — when he asks why she thought it was a good idea to have her kids read Philip Roth's very adult novel Goodbye, Columbus, she explains, "They'll gain an appreciation about Jewish men in their early 20s" — and life with Fran is ultimately no less messy than it was with Adam. In one episode, she discovers that Fran, who finds traditional porn depressing, keeps photos of his exes on his phone as a masturbation aid; indignant, she tells her friends, "I'm not going to be edged out by girls who don't even have interesting fat deposits on themselves!"

Marnie and Desi remain entertainingly awful (even her pronunciation of "Ecuador" is stomach-churning). The third episode, filmed mostly on location in Japan, is a fun showcase for Zosia Mamet. And Fran's dry and mostly sensible reactions to Hannah create a very different and often amusing dynamic from when she was with Adam.  But through the four episodes sent to critics, there's a sense that the show itself is struggling with the next phase of life as much as the characters are.

Early on, for instance, there's some flirtation between Adam and Jessa. It doesn't come out of nowhere, as the two were very much tangled up in each other's lives last season, but it still plays like the kind of mix-and-match romantic storytelling shows do at an advanced age when they're running out of stories to tell about certain characters. Similarly, Elijah (Andrew Rannells) finally gets a story arc of his own — getting involved with a famous news anchor played by Corey Stoll — after spending most of the series providing running commentary on Hannah's many bad decisions. Rannells has more than earned the belated showcase, but it comes at the expense of other characters like Ray (Alex Karpovsky), on a show that even at its best had difficulty servicing its supporting cast.

In other ways, though, maturity works to the series' advantage. We continue with the story of Hannah's father Tad (Peter Scolari) coming out late in life, and the impact it's having on both Hannah and her mother Loreen (Becky Ann Baker). More than at any point in the series so far, this development forces Hannah to be the grown-up in a situation, and while she's not always good at it, it's an excellent showcase for Dunham as dramatic actress.

Had HBO announced that this would be the final season, rather than one more a year from now, that might have also felt right. But Girls still feels like Girls, albeit a less surprising version than it was back at the start, and that bumpy transition into real maturity should provide some good material for everyone as the series moves through these last two years.

In the midst of one argument, Fran complains, "Hannah, you are being too much."

"I'm not being too much," she replies. "I'm being just enough!"

Hopefully, we'll all still feel that way by the time we get to the end of season 6.

Alan Sepinwall may be reached at sepinwall@hitfix.com

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com