My cousin is the perfect travel partner, despite being 15 years younger than me. On our first trip together, he taught me a valuable lesson.

• My cousin is 15 years younger and lives in a different country, but we're regular travel companions.

• When it comes to the travel partners, I've learned that an open mind is crucial.

• Together, we've been to Europe, Asia, the Middle East, and South and North America together.

I live in Australia, while my cousin Yonatan, who is 15 years younger than me, grew up in Israel then moved to the US after college. Despite the age and cultural differences, he was always the family member I was closest to. We got along well and he always felt like a younger brother.

I love traveling and I've been fortunate to have visited 107 countries. As a child, Yonatan would visit me in Australia and my travel stories always enthralled him. I promised him we would take a trip together when he graduated from college — never really expecting it to actually happen.

But when Yonatan graduated in 2012, he remembered and asked me to keep my promise. We agreed to meet in Oslo, Norway. At the time, he was 22, while I was 37 with two young twin sons. I didn't know what to expect and was worried that we'd want different things from our trip — maybe he'd want to sleep all day and party all night, and I would prefer to get up early and explore. I was concerned this trip could be a disaster.

My fears were confirmed on the first day after he wasn't at the hotel when I arrived and didn't respond to any of my messages. When he finally stumbled into our room 11 hours later at 4 a.m. and regaled me with a story of partying with locals before getting lost in a forest, I began to regret my decision.

I thought he'd want to party every night, but he ended up surprising me

It seemed like that first night had tired him out, and for the next few nights, we were in our rooms by 10 p.m. But I promised Yonatan that on the last night of our trip, we would stay out late and visit some bars. The night before we left, we returned to our room at 2 a.m. and were due to fly home the next day at 9 a.m. I was disappointed that we hadn't had time to visit Frogner Park, the world's largest sculpture park made by a single artist and one of the most recommended sites on TripAdvisor. It was also highly recommended by a friend who'd visited the park.

Yonatan suggested setting our alarms for 5 a.m., giving us two hours to explore the park before leaving for the airport. With only three hours of sleep, I worried I'd be too tired the next day to enjoy it, but Yonatan said something that has stuck in my mind ever since: "In a few years, you won't remember how tired you were, but you will remember the fun you had visiting Frogner Park."

At 5 a.m., we headed to Frogner, where we were the only people there. We enjoyed the sunrise and admired the sculptures, creating great memories I'll never forget. Despite the hiccup on the first night of our trip, I now knew Yonatan was a good travel partner.

Since that first trip, we have visited many countries together and become regular travel companions.

Yonatan plans to carry on the tradition

My twin sons are 16 years younger than Yonatan, and he made the same promise to them that I once made to him. Once they graduate college, they'll all take a trip together. My sons have seen the kinds of memories and experiences I 've created with Yonatan and are excited to do the same.

I know that the tradition will continue even beyond this. Last year, Yonatan had his first child, and, coincidentally, she's 16 years younger than my sons — it looks like they'll also have a promise to make!

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