It all started in a zoology class in 1934. Students were seated alphabetically in the tiered lecture hall, so John Henderson, 21, sat directly behind Charlotte Curtis. When he looked down, he liked the shy 20-year-old he saw in front of him.

And Charlotte?

“I thought he was just a fine fella, and I didn’t mind his looking over my shoulder,” she told The Washington Post in an interview.

On Dec. 22, the couple — she’s 105; he’s 106 — will celebrate their 80th wedding anniversary. The Guinness World Records have recognized the longevity of their love by naming the Hendersons the oldest living married couple.

John was born in 1912 in Fort Worth. He told The Post he remembers the first time he heard a radio; the neighbors brought one home when he was about 8 years old.

“And I well-remember that long antenna. They had to put it up from the front yard to the backyard to receive a radio show,” he said.

He moved to Austin to attend the University of Texas in the early 1930s, where he was a guard on the football team. (Hook ’em, horns!) At the time, about 53,000 people lived in the capital. Nowadays, the metropolitan area boasts a population of more than 2 million.

He recalls renting a room across the street from the Gregory Gym, one of the few historical buildings remaining on the urban campus.

“The neighbors next door had a cow and chickens. You can imagine today a cow and chicken house across the street from Gregory, where the campus is so large now you wouldn’t recognize hardly anything,” John said.

Charlotte was born in Iowa in 1914. When she was in her early 20s, her older sister’s husband was killed in a military plane crash. Charlotte’s entire family moved to Texas, where the husband had been stationed, to be with her sister and help out.

Charlotte soon enrolled at UT, where she met John. They met the same year construction began on the famous UT Tower. It wasn’t completed until after they had graduated.

There was also a height restriction barring buildings from being higher than the Texas Capitol. Today, the capitol dome is no longer visible on the skyline, depending on the angle.

Although short engagements were not unusual at the time, “it took her five years to make up her mind that she wanted to get married,” John said with a laugh. It was the middle of the Great Depression, and they wanted to earn some money before they set up a home, so Charlotte took a teaching job in the Houston area, and John coached football and basketball in Port Arthur, Tex.

John and Charlotte married in a tiny ceremony — only two guests were present — on Dec. 22, 1939. They honeymooned in San Antonio, staying at a hotel that cost $7 a night.

Although they have been together for 85 years, they have been married only for 80, meaning they do not hold the record for the longest marriage. That title, according to Guinness World Records, belongs to Zelmyra and Herbert Fisher, who wed at the ages of 19 and 17, respectively, and were married for 86 years and 290 days before Herbert’s death in 2011.

The Hendersons made their home in Baytown, Tex. Charlotte continued to teach, and John had a long career at Humble Oil and Refining Co. (now part of Exxon). He retired in 1972.

That’s right, they’ve been in their golden years since Watergate.

They have filled that time with travel, mostly cruises. They have sailed around South America, Scandinavia, China and dozens of other locales.

They have also stayed loyal fans of UT football, attending Longhorns games when they can. John, who is also UT’s oldest living former football player, has gone to at least one game per season for the past 84 years. That’s been easier to do for the past decade, since they returned to Austin to live in a retirement community.

John told The Post that his favorite invention that he has witnessed in his lifetime, besides jet engines, is television. He first saw one in a store window on a trip to New York City in the early 1950s and, within a few years, had one in the living room.

So what’s the couple’s secret to their longevity? Living in moderation, they said. They eat right, don’t drink much, and John still exercises at the community gym almost every day. Except for some hearing loss, both are in excellent health.

The Hendersons never had children, “so some people have said that’s really why we’ve lived so long!” John joked.

They haven’t decided what they’re going to do to celebrate their 80th — that’s the oak anniversary, if you’re curious — but the retirement village held a party for them earlier this month.

So, after 80 years, do they still argue, or have they figured it all out?

No, they don’t argue, John said. But if you’re looking forward to your marriage becoming more peaceful in your late golden years, take note: They never argued that much in the first place, John said, and have always made a point to settle things before bedtime.

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