Traveling to countries like Kyrgyzstan, Romania and Cuba, staying on a strict budget and spending lots of time thinking about Airbnb – that sounds like the lifestyle of student travelers on a gap year. In reality, it's the life of American couple Michael and Debbie Campbell, who have dubbed themselves "the senior nomads." Debbie, who is 62, told CNBC in Singapore that the couple's daughter planted the idea in their heads in 2012 after seeing that her parents had a list of countries they wanted to visit. While the Campbells were uncertain about whether they could afford to travel full time, their daughter suggested they could manage their accommodation costs by using Airbnb, an online platform for home sharing. The couple, who had been living in Seattle, looked up Airbnb offerings in the places they wanted to visit, organized a budget and left Seattle six months later. Now, they've been on the road for five years, visited more than 70 countries, stayed in more than 170 Airbnbs and even manage to blog regularly about their experience. With their ample experience as guests, the couple managed to get internships at the tech company last September, becoming Airbnb's oldest interns. While the Campbells are admittedly adventurous risk-takers, they didn't decide to retire and travel on a whim. "Money was a concern," said Michael, who is 72, adding that they had a retirement nest egg that they needed to spend very carefully. "I wondered at the beginning: Could we do this financially? Would we have the self-discipline not to spend money more than we should? And five years later, we're doing just fine." Here are some of their tips on how to retire as senior nomads.

Set a budget

Before embarking on their journey, the couple did "a lot of spreadsheets." They sold their cars, their boat and — two years later — their house. The Campbells declined to disclose the cost of their entire lifestyle because they said they did not want to discourage anyone from trying it out. "We're afraid people will say, 'I don't have that amount of money, I can't do it', but they can do it for less or more. They could focus on countries that are more affordable," said Michael. However, they shared that they worked on their budget with a financial advisor and decided to spend an average of $90 a night on accommodation.

Spend money on experiences, not things

The couple said the key to staying on budget is "don't buy things." That rule even applies to souvenirs, although they do buy gifts for others. "We've gotten so bad that if I see a greeting card I want to give to Michael, I take a picture and show him the picture on my phone," Debbie said.

Live like a local

But many of their best experiences have come for free. Debbie said the couple always tries to see the "free things" wherever they go because "that's the thing which locals see anyway." They get tips from their Airbnb hosts about events going on, but they look for free concerts at churches, free exhibitions at museums, and they also enjoy checking out public libraries. The couple also saves money on food by cooking many of their meals at home, going out for dinner just once or twice a week.

Keep a journal for expenses

One of the key strategies the Campbells use to stay on budget is to write a journal entry every day. Michael said that keeping track of their expenses had become a habit akin to brushing their teeth. The couple takes turns writing about their experiences in their journals, and tapes their receipts in the journal to keep track of spending.

Walk a lot

Debbie told CNBC she had been thinking to herself that "we've been gone five years, but I don't feel any older, but we are five years older than we left." They credit their energy and stamina to "walking a lot." "That's helped us with our health," she said, adding that they now walk a lot more than they used to in Seattle — where they drove more often.

Find an internship

Debbie and Michael said they watched the Robert De Niro movie "The Intern," and were so inspired by the tale of an older man finding purpose in his internship that they decided to ask Airbnb for a shot. While the internship was unpaid, the couple said the experience made them feel "so vibrant." "We couldn't wait to go to work, we stayed just as late as anyone else," said Debbie, who used to be a graphic designer. Working alongside much younger people, the senior nomads started their own project called "Hug," which stands for "Help uplift guests." They worked on a guest recognition program that helped the tech company show greater appreciation to guests using the platform.

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