A lot of girls that come from overseas for studying are around 18-21.
During that time, most of their parents provide them with income, so they don't really need to go out looking for a job.

It's probably around 21-23 when they start to spend more, and meet some friends who work in the industry, and then they start working as a ML or WL.

So it's quite rare to find a 18 year old, unless they came here to just bang or money, or rub their hands all over guy's backs.