On the first day of summer, just after dawn, Dale Sanders, 91, prepared to start the steep, rocky hike up to Franconia Ridge in New Hampshire’s White Mountains.

Mr. Sanders’s mantra might resonate with anyone in their tenth decade: “It’s a ‘don’t fall’ day today,” he said, slinging a small backpack onto his compact, wiry frame.

The roughly 2,190-mile Appalachian Trail runs from Georgia to Maine. Mr. Sanders had been chipping away at it since September, in a bid to reclaim his record as the oldest person to hike the full length. (His goal is to complete a thru-hike, by walking the entire trail in a 12-month period.)

He was roughly 70 percent finished, but some of the toughest miles were ahead. I joined him for two especially challenging days.

The White Mountains are known for extreme weather, and Mr. Sanders said he had been turned away by a concerned trail steward during a heavy storm the previous week: “He said, ‘You know, you’re going to die if you keep going.’”

The weather had calmed somewhat, but soon after he emerged above the tree line and began his traverse of the ridge, roaring gusts of wind brought dense fog and sharp, sideways rain.

The route frequently requires hikers to scramble. As he reached the bottom of a rock slab, he realized he had no memory of this obstacle from the last time he had hiked the trail. That was in 2017, when, at 82, he first set the record. After carefully climbing the ledge, he estimated the hike was twice as hard this time.

Thru-hikers typically use trail names; Mr. Sanders is better known as “Grey Beard.” That morning, he had set out with an experienced 28-year-old hiker from Georgia, Garrison Gandy, or “Doublewide,” who had been crashing at the same hostel.

Despite the conditions, the pair made steady progress toward the day’s goal, an off-grid shelter eight miles down the trail where a hot meal and a bunk were waiting.

The next morning, the first hour of hiking was strenuous — a steep mile to the summit of Mount Lafayette. Mr. Sanders lamented that despite hard training, his fitness hit a ceiling that hadn’t existed in earlier decades. “I wanted it to be pretty close to where I was in 2017, and I’ve never reached that,” he said.

As he caught his breath on the summit, the clouds had cleared, revealing a sparkling view of the Pemigewasset Wilderness.

12 Miles a Day

It was the allure of setting a record that first drew Mr. Sanders to the trail.

Mr. Sanders, who lives with his wife near Memphis, Tennessee, retired in 2002 after a career working in parks and recreation for the Navy. He marked his 80th birthday by becoming the oldest person to paddle the full length of the Mississippi River, and soon began searching for other age records.

He learned he could set a record by completing the Appalachian Trail. Though he had never spent extended time hiking, his competitive streak was activated.

Mr. Sanders credits this part of his personality to being bullied in school while growing up on a Kentucky tobacco farm, and the escape he found through sports.

“I wasn’t good in the books,” he said. Physical activity, on the other hand, “gave me something real.”

His first Appalachian Trail age record was broken in 2021 by a hiker named M.J. Eberhart, trail name “Nimblewill Nomad.” Mr. Sanders befriended Mr. Eberhart that year and encouraged him to set a new mark.

“He was going to quit several times,” Mr. Sanders said. “I actually went up and hiked with him the last few days so that he wouldn’t quit. We’re really close friends.”

Still, Mr. Sanders wanted the record back. For the current attempt, he planned to hike 12 miles a day, with one day off a week.

Most thru-hikers tackle the trail from the south to north, starting in Georgia and ending in Maine. But as long as Mr. Sanders walks every section of the trail, he can do it in any order and direction he chooses.

To maximize the year’s hiking weather, he began his hike headed south from Harpers Ferry, West Virginia, then returned to that spot to complete the northern half.

While most thru-hikers sleep in a tent or in lean-to shelters, Mr. Sanders prefers his truck camper, a simple shelter, labeled “Base Camp on Wheels,” that sits in the bed of a pickup truck. It’s driven by a rotating cast of volunteers, who also cook his dinner and help plan the next day’s mileage. For the first 800 miles, one driver was Mr. Eberhart, now 87, who’s helping to break his own record.

Two friends from his Mississippi River descent, Craig and Katie Heaton, a married couple in their mid-60s, are also among Mr. Sanders’s crew.

“He won’t tell you how to live your life,” Ms. Heaton said, “but he shows by example, and I think that’s what touches me the most.”

Selfies and High-Fives

Mr. Sanders’s appetite for continuing to push his limits in old age has earned him many fans along the trail.

Emma Bartlett — also known as Comfy — had been hiking since March when she paused for a picture as she passed Mr. Sanders on the climb up to Franconia Ridge. “Everyone has been talking about you since Georgia,” she told him.

“If I’m even walking at 91, I will be jumping for joy,” said Ms. Bartlett, who is 23.

Mr. Sanders is comfortable hiking alone, but he would always prefer company. As we parted ways, he found an impromptu hiking partner to accompany him for the next leg.

Nicholas Loukides, 29, who has hiked in the White Mountains since he was in grade school, said the chance to tackle a few miles with Grey Beard was a highlight of his trip. “Every mountain I climb,” he said, “I’m like, ‘Dude, you did this?’”

There are formidable obstacles remaining, like Maine’s 100 Mile Wilderness, the trail’s most remote stretch, where there will be very few opportunities for supplies or crew assistance for days. And Mr. Sanders still has to finish a section of the Smoky Mountains in North Carolina. But if he continues at his current pace, the age record will be his again before his 365-day deadline.

Mr. Sanders said he plans to finish, even if he runs out of time for it to count officially. Either way, he said he will soon have to look for a new record: “I’m not going to stop unless physically I simply cannot do it anymore.”