Probably at Birth!
Actually, I was born in Iran in the early 60's to American parents. My father was an Engineer on a 3yr assignment. Growing up I would watch home movies my father took of the journey going over, while residing, and our two week return via Europe.
As a kid I would ride my bike endless miles through the New Jersey suburbs, and loved riding in the car with my family throughout the Eastern Seaboard and Midwest.
At 13yrs, I joined some family members on a 3wk trip to Europe, specifically France to visit family. I can still remember all the details. I was hooked after that trip! College even took me out West and to this date I'm at about 50 countries and counting!