It used to be that mid-life crises were the kind of thing that could make a person feel like their life was over and there was no hope to make things better in the rest of their lives. But with the ever-expanding financial power of the Baby Boomer generation wielding greater and greater influence, attitudes are shifting in a major way and Hollywood is starting to reflect that with its offerings.

Jane Fonda in particular, at age 80, has found huge success the last three years on the Netflix sitcom “Grace & Frankie,” and she’s likely to find big success at the box office this weekend as well with the solid comedy “Book Club.” The story of four women (the others are Diane Keaton, Candice Bergen and Mary Steenburgen) who are lifelong friends with a monthly book club, and the comedic upheavals they experience when they read the “Fifty Shades of Grey” trilogy, it’s a solid comedy that gives its ace cast of veterans a chance to shine.

At the same time, Melissa McCarthy is also addressing a similar theme of reclaiming one’s magic in middle age with her latest comedy “Life of the Party,” which opened to so-so business last weekend. The story of a frumpy suburban mom who goes back to college alongside her freshman daughter after her husband abruptly dumps her, and finds excitement in the school’s party scene and a torrid fling with a hunky student, “Life” has some huge laughs but overall falls flatter than a three-day-old keg of beer.

In “Book Club,” Fonda plays Vivian, a powerhouse businesswoman who never married, opting for a string of affairs after breaking up with the one great potential love of her life, Arthur (Don Johnson). Bergen plays Sharon, a federal judge who hasn’t dated in the 18 years since she divorced, but now faces the awkward dilemma of a dual engagement party for her son and her ex-husband, who’s now engaged to a much younger bimbo.

Rounding out the foursome are Keaton as Diane, a recent widow whose two grown daughters are constantly over-protecting her from life, and Steenburgen as Carol, a long-time married woman whose husband Bruce (Craig T. Nelson) has lost his ability his sexual prowess and consequently his zest for life. When Vivian declares that her pick for the ladies’ book club is the “50 Shades” trilogy, reading about the salacious sex life of its couple throws a spark into their lives.

Carol jumps into online dating, with hilarious results coming from an evening with George (Richard Dreyfuss), while Vivian runs into Arthur again and has to weigh whether it’s time to finally stop running. Diane has a hysterical meeting with a wealthy pilot named Mitchell (Andy Garcia) but is afraid to let her daughters know she’s intrigued by another man just a year after  her husband’s death, and Carol tries everything from dance lessons to slipping Bruce a Viagra to wake him up.

“Book Club” has some significant charms, as it brings together eight enormously appealing actors who don’t land the big roles anymore and gives them a fun situations to play in. It’s the kind of movie that will make you grin throughout and laugh pretty often, while keeping the schmaltz under control.

However, it’s also very predictable , with co-writer/director Bill Holderman rotating the four couple’s stories over and over throughout. But for those who prefer character-driven stories over superhero  smackdowns, this is one “Club” you’ll want to join.

Whereas “Book Club” makes its female foursome eminently relatable, “Party” ultimately fails because of the fact that no rational human being would act like any of the characters in the film. McCarthy’s Deanna goes from being a frumpy loser to party-loving wild woman simply because her daughter Amanda (Adria Arjona) puts some new lipstick on her, adds a little pizzazz to her hair and rearranges her top to show some cleavage.

Deanna and Amanda both wind up sneaking out of frat boys’ rooms the next morning, with Deanna revealing that she had a rowdy night with a hunky guy named Jack (Luke Benward), who can’t stop texting her and pushing her further into a fling. As her ex-husband Dan (Matt Walsh) quickly announces his engagement to stunning real estate magnate Marcie (Julie Bowen), Deanna has to decide when she’ll stop being a doormat and start making some big steps of her own in life.

“Party” has a few very funny scenes, particularly a restaurant showdown with Deanna taking on Dan and Marcie that leads to a big surprise, and an awkward classroom presentation in which Deanna’s nerves make her sweat so much she appears ready to drip right off the screen into the theater. But overall, only Deanna and her best friend Christine (Maya Rudolph at her best) register as fully developed characters, with everyone else either flat or constantly changing their personalities to earn cheap laughs.

Worst of all, the movie feels like it reached its logical conclusion at 80 minutes and the filmmakers opted to pad it out another 25 minutes so that viewers wouldn’t feel shortchanged. McCarthy co-wrote this with her husband Ben Falcone, who also directs, but the pairing isn’t a fruitful one. Their prior two films together as co-writer and director, “Tammy” and “The Boss,” were her only non-blockbusters to date, making one wish that McCarthy would find someone else to party with when making actual movies. n

“Book Club” GRADE: B

“Life of the Party” GRADE: C