They asked for the 10 years or from the age of 18.
It's travel history for the last 10 years, or since the age of 18,
whichever comes first. That's they key piece of info.
What that means in practice is that if you're 27 years old for example, that means that 10 years ago you were 17 years old. So you won't include travel history for when you were 17 to 18 years old. You will include travel history starting the age of 18.
If however you're say 29 years old, that means that you were 19 years old 10 years ago. So you'll include travel history for the past 10 years, meaning back until the age of 19.