The old chestnut about the bond that develops between a lonely teenager and an elderly gent from the neighborhood he’s thrown into contact with—who, of course, has a terminal illness—is used to modest effect in Tony McNamara’s “Ashby,” a semi-engaging coming-of-age story with a smidgen of action-movie violence added to the mix that’s a far nicer version of “Apt Pupil.”

Mickey Rourke plays Ashby Holt, a crusty sort who’s just been informed he has only weeks to live and nearly wrecks his car (and do a lot of damage in the process) driving home. He’s soon visited by Ed Wallis (Nat Wolff), the kid who’s just moved in next door with his divorced mom June (Sarah Silverman). Ed, an intelligent, articulate but rather cocky fellow, has been assigned by his snarky English teacher to write an essay based on conversations with “an old person,” and though Ashby is in no hurry to talk about his past (or admit to being old), he has a change of heart when he learns that Ed has a driver’s license and could serve as a ready-made chauffeur in his declining days.

As it turns out, Ashby does need someone to drive him around—and not simply to the doctor. He’s an ex-CIA assassin, and has just found out that he’d been conned by three of his former associates into including among his ninety-odd kills one fellow who was no enemy of the USA but merely a guy interfering with his colleagues’ money grabs. Seeking absolution for his sins (something he discusses with his parish priest), he decides to redeem himself by rubbing out the nefarious trio who had misled him into offing an innocent man. And he needs Ed to drive him to confront them—though the kid won’t know the reason behind the trips.

By this time Ed has discovered Ashby’s colorful past and accepted that he won’t be able to include it in his school paper—which will depict his subject as a retired vacuum cleaner salesman. But after some initial trepidation he’s come to admire Ashby all the same. Besides, he has other matters on his plate. He’s determined to become the star receiver on the school football team though he’s hardly stellar pigskin material and there’s already a fellow in that position, and is looking to deepen a relationship with smart-girl classmate Eloise (Emma Stone). He also has to deal with his man-hungry mother’s string of feckless dates and with his absent father’s inability to find the time for them to get together outside of Skype. No wonder it takes even such a bright boy a lot of time to figure out what Ashby is up to on their rides into the country.

It’s takes a delicacy of touch in juggling lighthearted teen material with action-movie violence that McNamara doesn’t quite possess–a scene that juxtaposes Ashby’s pursuit of one of his quarries with Ed’s celebration of patching things up with Eloise is simply jarring–and his script has so many plot threads spinning at once that the seams come to seem terribly frayed. But “Ashby” is buoyed along by the leads. Rourke uses his hangdog looks and world-weary manner to good effect here, and actually brings a measure of poignancy to the role. And if Wolff overplays the bright, eager beaver a bit much, he still cuts a likable figure, even in scenes on the football field that are barely credible. And if Silverman is oddly colorless as Ed’s mom, there’s compensation in Stone’s turn as his ion-and-off girlfriend. Kevin Dunn, moreover, makes the school coach a more engaging fellow than is often the case, and Michael Lerner can always be depended on to make an impression, this time as one of Ashby’s prospective victims. The technical credits are solid enough for a movie made on what must have been a fairly low budget, with Christopher Baffa’s widescreen cinematography more than decent and Matt Friedman’s editing okay despite the abrupt shifts among storylines.

“Ashby” winds up a small, familiar but reasonably engaging coming-of-age dramedy that wouldn’t be worth a trip to the multiplex but should prove a decent time-filler in other formats.