Every decade in a person’s life is a milestone. At 10, a child rejoices at reaching double digits. At 20, he’s no longer a teen. From 40 to 60, he’ll compile charming Hallmarks about the joys of growing old. But upon turning 70?

“Threescore years and ten,” said Mark Twain at his 70th birthday celebration. “It is the Scriptural statute of limitations. After that, you owe no active duties; for you the strenuous life is over. You are a time-expired man, to use Kipling’s military phrase: You have served your term, well or less well, and you are mustered out.”

Not so for Ed Ott and Bill Irwin, fast friends who traveled from their home near San Diego to Calais, Maine, to celebrate their 70th birthdays by bicycling 1,900 miles down the East Coast.

Their journey started on Sept. 12 in Calais, and has already inspired donations for a wide variety of causes.

“Both of us have been active all of our lives,” said Irwin in a recent phone interview. “It’s a mindset, and you really have to keep after it.”

They call the trip the “Victory Tour.” It is the fourth of part in a longer bike ride, one that will create a box around the edges of the United States.

“We’re complete idiots to do this,” said Irwin after their warm-up bicycle ride Down East on Tuesday. “It started out in ’04, when we went across the top of the country, and we thought that would be it. I don’t know how it got so out of control.”

In 2004, the pair biked from Washington to New Jersey. Then in 2007, they pedaled down the West Coast. And in 2010, they biked from San Diego to Jacksonville, Fla.

“This is probably the last ride we’re going to do,” Ott said. “It’s really a victory for us.”

Since the first long ride, they have encouraged people to support them by donating to various causes. The three rides combined raised about $50,000, much of which was donated to San Diego United Methodist Church (of which Ott is a member) and the Torrey Pines Rotary Club in La Jolla (of which Irwin is a member).

The East Coast ride is dedicated to their friends’ wives: Mary Allan, who is battling ALS, commonly known as Lou Gehrig’s disease: and Berry Hughes, who is battling cancer. Donors can choose to give to the ALS Therapy Development Institute, the American Cancer Society, or whatever other organization or institution is important to the donor.

“We pay all of our own expenses,” Ott said. “You make a pledge to whatever charity you want.”

Irwin aims to raise $19,000 ($10 per mile) for the Torrey Pines Rotary Club Foundation, which supports local and international causes, from purchasing toys for Rady Children’s Hospital in San Diego to providing tsunami disaster relief in Japan.

Aside from that, the two friends are simply riding for the fun of a challenge.

Ott and Irwin met 30 years ago as members of Old Mission Beach Athletic Club, a San Diego-based nonprofit organization with 440 members that brings members together to engage in sports such as long-distance running, volleyball, rugby and surfing. Both men were marathon runners earlier in life.

“At least for me, about 15 or 16 years ago, my knees said, ‘We don’t want to do this anymore.’ And I said, ‘Well, I still need to exercise,’ so I started getting on a bike,” Ott said.

It’s only natural that his cycling, like his running, turned into a long-distance sport.

“The first thing we say when people ask us why is, ‘Because we can.’ It’s an accomplishment, just a neat opportunity,” Ott said. “We have three different guys [from Old Mission Beach Athletic Club] who drive a truck in support of us. It’s kind of like a road trip.”

From Maine to Florida, the pair will create their own route, mainly following Routes 1 and 1A, and asking local residents about road conditions along the way. They’ll ride as close to the coast as possible, said Ott, not for romantic views of the rocky shore or the salty breeze but because along the coast, roads tend to be less hilly.

Irwin will keep people updated on their whereabouts on his blog at torreypinesrotary.org/bikeride.html.

“Yesterday — no, the day before — we were leaving Springfield and there was a map in [a rest stop] lobby of the New England states in 2012,” said Irwin. “We opened it up and the eastern part of Maine was not even included. This tells us something.”

The next day, they were reassured that Calais, Maine, did indeed exist when they rolled into town and stopped for dinner at Townhouse Restaurant, where they shared beer and conversation with fellow customers. Someone even covered their bill.

They plan to enjoy the sparse population of Maine, because they anticipate that one of their biggest challenges on the East Coast will be the heavy traffic and busy metropolitan areas. They aim to ride about 50 miles a day, enjoy a few rest days, and end their trek on Oct. 23 in Miami, Fla.

“I remember the big disappointment of the first trip was that we couldn’t be riding around and looking at scenery the whole time,” Ott said. “You have to be looking at the road and making sure people see you.”

Overall, the pair seemed confident and carefree and they headed into their final leg of their nationwide bike ride. Though they do have one big concern.

“In general, after we’ve ridden for about 50 miles or so, we like to have a beer,” Ott said. “And sometimes, it’s tough to find a good tavern.”

To show your support of the “Victory Tour” by donating to a charity, email Ott at edwardott@yahoo.com or Irwin at wirwin@SBCglobal.net. Follow trip updates at torreypinesrotary.org/bikeride.html.

Aislinn Sarnacki is a Maine outdoors writer and the author of three Maine hiking guidebooks including “Family Friendly Hikes in Maine.” Find her on Twitter and Facebook @1minhikegirl. You can also...