But, it can happen for a variety of reasons, including mental illness, illness or other issues with family that result in the loss of a position. Did you ask this delivery guy why he's doing this job if he used to be a chemist? Believe it or not, sometimes people get tired of doing these kinds of jobs and decide instead to do something less stressful. I don't know how old "15 years your senior" is in this instance, but it could be a retirement job or a side hustle to get him through a rough patch. Who knows.
Can it happen to you? Certainly, it could happen to anyone without generational wealth. That is, if you don't have 6 figures invested and generating passive income, you could very well end up doing a low paid job for a long time. Plan accordingly: network, keep up to date with hot skills, and/or marry rich.