“The Nanny” star Fran Drescher returns in the May/December romantic comedy “Living With Fran” (7:30 p.m., WB).

Drescher’s eponymous character is recently divorced from an unseen husband and living with her look-alike teen daughter Allison (Misti Traya, “Joan of Arcadia”). While that would be enough material for most sitcoms, “Fran” revolves around Fran’s torrid relationship with her new live-in boyfriend Riley (Ryan McPartlin, “Passions”), a handyman she met while embarking on her new post-divorce career as an interior decorator.

Riley is handsome, sensitive and attentive. And he also happens to be 26 years old, while Fran is old enough to have watched the Beatles on “The Ed Sullivan Show.” You do the math.

The subject of Riley’s tender age becomes more apparent when Fran’s 21-year-old son Josh (Ben Feldman) returns to the fold after suffering a nervous breakdown and dropping out of medical school. This is supposed to be funny. In addition to Fran’s new boy toy, Josh also discovers that his mother has adopted a strange musician Duane (Branden Williams), who is living in the closet of the gym that used to be Josh’s bedroom.

For those keeping score, this marks the second sitcom of the year with a “strange guy living in the closet” subplot. Tom Poston appeared on “Committed” as a dying clown living in Marni’s apartment. Let’s hope it’s not a trend.

Fans of “The Nanny” will be sorely disappointed. On that show, Drescher’s loud and obvious pursuit of the urbane Mr. Sheffield set the stage for years of pratfalls, outrageous outfits and a graduate-level course in Yiddish slang. Now, “Fran” already has her man. What’s so funny about that? It doesn’t help that the affable Riley has all of the edge of a Labrador retriever.

Drescher seems to be counting on her audience to root for a woman of a certain age who has retained her youthful figure, amorous vigor and girlish attitude. And while this premise might play well for the duration of a Lifetime movie, it’s an odd story for a weekly sitcom — particularly on a network with a large audience of teenage girls and their mothers. It’s one thing for us to root for the elder “Gilmore Girl.” But would that show survive if Lorelai started playing with boys Rory’s age?

Riley’s Oedipal fling with Fran looms large in the show’s second episode (8:30 p.m., WB) when Fran invites her lover’s parents, Tom (John Schneider, “Smallville”) and Donna (Marilu Henner “Taxi”), over for dinner. The gang winds up in the hospital waiting room when nervous Riley cuts his finger while carving the roast, and Fran and Donna compete over who gets to “mother” the wounded boy.

Tonight’s other highlights

• God-given chores on “Joan of Arcadia” (7 p.m., CBS).
• Jordan takes an important step towards manhood on the season finale of “Bernie Mac” (7 p.m., Fox).
• Suspicions fall on a bombing survivor on “JAG” (8 p.m., CBS).
• Awkward partners on “Third Watch” (8 p.m., NBC).
• Jack finds Marwan’s lair on “24” (8 p.m., Fox).
• A bank robber’s pattern emerges on “Numb3rs” (9 p.m., CBS).
• A fool for a client on “Law & Order: Trial By Jury” (9 p.m., NBC).
• Scheduled on “20/20” (9 p.m., ABC): an interview with Rosie O’Donnell.

Late night

Jimmy Fallon, Emily Van Camp and The Four Tops appear on “Late Show with David Letterman” (after Masters golf highlights, 10:50 p.m., CBS) … Jay Leno is host to Paul Newman and Breakin Benjamin on “The Tonight Show” (10:35 p.m., NBC) … Charlie O’Connell and Dizzee Rascal appear on “Jimmy Kimmel Live” (11:05 p.m., ABC).

Jimmy Fallon and Sarah Vowell chat on “Late Night with Conan O’Brien” (11:35 p.m., NBC) … Craig Ferguson is host to Sam Elliott and Amy Yasbeck on “The Late, Late Show” (11:37 p.m., CBS).