At age 64, I remain convinced that deep in the soul of every middle-aged man, there’s a 12-year-old boy who never grew up.

That’s why grandpas still crack gas-gags with their grandsons. And it’s also why Dav Pilkey’s riotous “Captain Underpants” books were a hit with kids and grown-ups alike. (After all, that series features a villain named Hairy Potty — and a dreadful “attack of the talking toilets”!)

Since my own inner “tween” is especially precocious, I laughed my head off at Dog Man — the animated DreamWorks hit based on Pilkey’s popular follow-up to the “Underpants” series.

Both the “Captain” and the “Dog” — along with yet another burgeoning Pilkey franchise called “Cat Kid” — are goofy graphic novels supposedly concocted by two deranged fourth-graders whose artistic prowess is just a step or two above stick figures. These manic tales are bursting with action, color, lunatic invention and uproarious mayhem.

Having enjoyed “Captain Underpants” with my own kids years ago, I was pleased to discover that in the recent “Dog Man,” Pilkey has gotten more heartfelt and touchy-feely — without abandoning his comic irreverence.

At a fast and flamboyant 89 minutes, Dog Man captures both the sky-high hilarity and the down-to-earth sentiment in a film that’s sure to score with both kids and parents. Though the jokes are admittedly silly and sophomoric, I haven’t laughed that hard in years.

The titular character has been cobbled together through some unlikely surgery: A pair of dog-and-cop partners — having failed to defuse a bomb set up by “the world’s most evilest cat” — were cobbled together with a canine head and a human body.

In this first film foray, the resulting policeman — who cannot talk but is great at sniffing out crime, ha ha — spend most of their time trying to keep Petey the Cat in jail. For the rest of the story, writer-director Peter Hastings has wisely jettisoned the slap-dash plotting in Pilkey’s first volume, reaching ahead to a later installment for a genuinely touching father-son dynamic with Petey and an adopted kitty (plus an absentee parent who seems to have left Petey scarred for life). All this is handled with just the right light touch — so we can tell, among other things, that Petey’s “kill-all-do-gooders” motto is going to backfire spectacularly.

Swirling around this plotline is a cyclone of outlandish grade-school comedy involving buildings that come to life and start fighting; an 818 phone number that politely informs you, “Life’s not fair”; a vacuum cleaner sucking up the ocean; a shop whose sign indicates that its two public states are “open” and “go away”; another store called “Explosives and Things” — which is, of course, having a “Blowout Sale”; edifices with names like “The Major Hospital in Town”; a dead titanium fish that gets resurrected with “living spray”; and a robot with the irresistible monicker “80 HD.”

The business with the dollar bill kept me chuckling for hours; and the closing credits feature a bit of Pilkey’s famed “Flip-o-Rama,” by which he brings a modicum of real animation to his hardcover books.

All this should provide some idea of whether or not Dog Man is your cup of kibble. In any case, I herewith offer one final encomium, which I overheard from a boy heading out of the theater with his mom: “I can’t wait to see that again at home.”

Either he loved the movie as much as my friend and I — or maybe he just missed a bunch of jokes because the two of us kept laughing so loud.