Harmon Killebrew was Washington’s original Bryce Harper. Both signed record bonus contracts at age 17. Both had their power compared immediately to Mickey Mantle. Both hit drives measured at more than 500 feet as teenagers. Both were extreme personality types — Killebrew the introvert, Harper the extrovert — who needed maturity. And both were awaited in D.C. with great debate about “how you develop a superstar” from the instant they tore up the Sally League in their first year in A-ball. Yes, same league, almost an identical slugging percentage, but 55 years apart.

Anticipation for The Killer in the late ’50s rivaled the lust for Harper now. But the interminable five-year wait for his arrival as a Senators regular puts the impatience of the current Bryce Bulletins to shame. Killebrew homered in the majors at 18, and at 19 against the Orioles, he hit the longest blast in Memorial Stadium history at 471 feet. Stop torturing us, fans pleaded, by sending him back down to Charlotte, Chattanooga and Indianapolis!

Yet there’s a lesson in proper prodigy grooming in the Killebrew tale. When he got to Washington for good at 22, he was ready, tying for the American League lead with 42 homers his first full season. And he wasn’t prepared just when he was in the batter’s box. Killebrew, who died Tuesday at 74, not only hit 573 homers but will be recalled as one of the finest gentlemen in all of sports, not just baseball’s Hall of Fame.

Whatever can possibly be meant by the word “maturation,” Killebrew achieved it. We are left with the memory of a magnificent career and a man who was loved for his humility, kindness and charity with his “Miracle League” for children with physical and mental challenges. He was at ease and open, almost ego-less, whether with the biggest stars, a U.S. president who came just to see him play or the guy picking up his dirty uniform.

Once, asked what he did for excitement, Killebrew said, “I like to wash the dishes.”

When the Nats think about Harper’s career and life arc over the next few years, they should remember Killebrew.

“There couldn’t be two more opposite people,” one veteran baseball executive said. “I can guarantee you Harmon Killebrew never wore eye black above his shoe tops.”

As opposite as ’50s Idaho and 21st-century Las Vegas, but both in need of time. Harper has had shows of temper or pride and hasn’t rubbed everyone the right way. His base running, like Killebrew’s fielding, is zany. Is he adult enough to handle what’s waiting for him?

Such skepticism is nothing compared to what Killebrew faced. At 17 he got $30,000 — more than the Senators’ Roy Sievers earned ($26,000) after winning the ’57 home run title. Sievers was not jealous, but plenty of players, making peanuts in ’54, were.

From little Payette, Idaho, where his dad was the sheriff, Killebrew was forced by “bonus baby” rules to be on the Nats’ big league roster for two full years.

As a result, he was high-paid teenage baggage, dragged all over America, holding a job that somebody in the minors craved. Killebrew hit only .205 in 127 at-bats in those two years. Now, hecklers yell “overrated” at Harper. Killebrew heard it, too.

Once Killebrew was allowed to go to the minors, the Senators developed him patiently. After 70 games in A-ball in ’56, where he slugged .629, he won the home run title (29) in Class AA in ’57 despite playing in cavernous Chattanooga where he became the only player ever to hit a ball over the 470-foot sign in center field. In ’58, he played another 124 games in the minors. “We want Killebrew,” wailed D.C.

But, each year, all we got were late September call-ups, a few titanic home runs and word from The Post’s Shirley Povich and Bob Addie that Harmon just wasn’t quite ready yet.

He made errors that would be mocked in the majors. He struck out. Would crafty big-league pitchers junk-ball him and stunt him permanently as a hitter? Was he prepared for big-city life? He sure looked ready to us 10-year-olds in the unreserved grandstand.

In hindsight, the Senators, who weren’t good at much, actually had a sensible handle on how to help Killebrew grow into an adult. No doubt his family’s strength was his core. His grandfather was said to be the strongest man in the Union Army (he won all available heavyweight wrestling titles). His father was a college football star, and Harmon was a high school all-American quarterback with an Oregon scholarship offer. The discipline was there. But who knows if those five years of delayed stardom, all that paying dues, allowed him to keep his modesty and maintain a sense of balance about himself?

Maturation means something different for everybody, and surely for every teen prodigy. The oldest story, they say, is: “Life attacks man at flaw line.” With Killebrew or Harper, now hitting .366 at Hagerstown, raw talent is the area of strength. But where is the flaw line? Nobody escapes.

Wouldn’t it be decent, wise or just good business to let a teenager have a little while longer to find it, work on it and shore it up?

Nats GM Mike Rizzo is aware of the Killebrew-Harper analogy. Though the bonus baby years should be thrown out, Killebrew’s 338 games in the minors aren’t irrelevant. While a few teens such as Alex Rodriguez arrive with half that experience, such speed is only justified if everything goes flawlessly.

“Harper needs his time in the minor leagues. He needs to show these guys [in the Nats’ locker room] that he has paid his dues,” Rizzo said. “He still has things to learn, on and off the field. When he does come up, if he has [difficulties], you do not want it to be because he wasn’t developed properly.”

As baseball celebrates Killebrew, let us underline what might be most unusual about him: For once, a wildly celebrated teenage athlete managed, both as a player and a person, to have a finish worthy of the start. Give Harper the same chance.