PT74.S4.Q18 - A large study of people aged 65-81 and suffering from insomnia

treypark17

I had a quick question about a line of reasoning regarding the correct answer to this question. I got the correct answer, E, but for a different reason than what was explained in the explanation video. In the video, the narrator discusses the difference between old people and old people with insomnia and claims that this is where the sample is unrepresentative. However, when I was thinking about this question, I was focused on the phrase "as they age" and the fact that the sample size was those aged 65-81. I thought that it was too difficult to determine that melatonin was produced less as you age because what if it is produced at a lower rate during early years as well, but the sample only included older people? Would this line of reasoning be incorrect? Is this a type of thinking anyone else had?

Admin Note: Edited title. Please use the format: "PT#.S#.Q# - brief description of the question"
Link to explanation video: https://7sage.com/lsat_explanations/lsat-74-section-4-question-18/