Harlem girl, college-bound, entirely too smart for the neighborhood guys who are all “speak ‘game,’ play game, one big game” with their come-ons.

But then Ayanna, the aspiring writer and would-be poet, stumbles into Isaiah, the earnest, smart would-be music producer.

And before you can say, “Uh oh, here’s a white girl,” before you can mutter those three magic letters — “E.P.T.” — this summer romance takes the turn you just knew it would, dammit.

But it’s where “Premature” and director Rashaad Ernesto Green take us after that cliched first and second act that mark this indie drama as “must see.” Reworking a short film he did over a decade ago, sharing a co-writing credit with his muse and star, Zora Howard (also a star of the 2008 short film), we’re immersed in lives, a world and dreams that won’t be just “deferred” if Ayanna (Howard) loses her way. They will be derailed.

Ayanna narrates, in voice over, her feelings about her Harlem life and the swept-off-her-feet interruption that Isaiah (Joshua Boone) becomes.

She’s content to spend this last summer before enrolling at Pennsylvania’s Bucknell U. with her girls, a brassy quartet who make a big show of ogling the “talent” on the park basketball court. They use safety in numbers to keep the teenage boys on their heels, despite their sexual bravado and blunt and cute/crude pick-up lines.

“I got a THING for ‘thick’ girls!”

Look over Shonte (Imani Lewis) or Tenita “T” (Alexis Marie Wint) on the train, and Ayanna is the one who’ll call your bluff when you try to get off at your stop.

“Y’ain’t get number yet.”

She keeps a notebook with her, wears glasses to denote her bookishness, and insists on fidelity from her feckless would-be suitors.

“Is that your girl?”

“We still chill, right?”

“Go chill with her!”

She wears her long braids and glasses like armor and is quick with a brush-off if there’s unwanted attention. If she wants to be cruel, she lets the sweet-talker get deep into his game before dismissal.

But Isaiah has an offhand charm, speaks lovingly about his dead musician father, his musical aspirations, about how his Mama lectured him on which side a gentleman walks on when escorting a young woman down the street.

Ayanna is smitten, a tad too quickly and a bit too overwhelmingly. But that’s what teenagers do, right?

There’s a line she writes that somewhat sums up the movie and its biggest shortcoming. “We were too young to live this old.”

Everybody and I mean EVERYbody seems entirely too old for the high school-or-just-out-of-high-school world this population lives in.

Ayanna’s poetry about her first big love is polished and adult. “What did I know of my heart before you gave it shape?”

An African-American filmmaker has license to make stereotypical points about inner city kids “growing up too fast,” sexual young men bragging about their babies, very young women hectoring each other not to fall for this one or that one, to learn to “close your legs” if you’ve already had two children before hitting 20.

But making Ayanna 17 when the actresses playing her and her peers are plainly older, street-wise and world-weary, is a blunder. Up everybody’s age by suggesting Ayanna is finally ready to go to school at say, 22, and the picture might work better.

The life around them is deliciously filled-in, with Green and Howard plainly taking their cues from early Spike Lee films in fleshing out the cast and giving them something funny, sassy or slangly to say. Ayanna’s single mom (Michelle Wilson) and her friends — some of them much older — are just as comically crass in the sex talk department as their kids or grandkids are on the other side of the park.

“Who would you ‘give some’ too? OJ, Ike or CROSBY?”

Williams, playing a lonely woman who has drifted from man to man with no relationship sticking, comes off as self-involved, but is still capable of mothering moments when it counts and she’s warning her child about “chasing after those good-for-nothing boys.”

The performances and the milieu, with its colorful colloquial speech and loving if blundering sisterly relationships, is what sells “Premature” and makes it an indie film well worth your time.

It won’t seem wholly original to anybody with “She’s Gotta Have It” and “School Daze” burned into memory. But it’s a lively, lovely and lived-in slice of Harlem life that looks, sounds and feels “right,” even when what we’re seeing is over-familiar to the point of cliche.

MPAA Rating: unrated, explicit sexual content, nudity, alcohol, marijuana involving teens, and profanity

Cast: Zora Howard, Joshua Boone, Alexis Marie Wint, Imani Lewis and Michelle Wilson

Credits: Directed by Rashaad Ernesto Green, script by Rashaad Ernesto Green, Zora Howard. An IFC release.

Running time: 1:30