If they decline to take your answers when they realise you're in your 40s, it might well mean they already have enough data on 40-somethings (either cos many have already filled in the survey, or from past research).
Chances are, they know people in their 30s and beyond have a fair bit of disposable income, and will buy most big packs sooner or later -- but people in their teens have less cash to throw around, so it's important to work out what packs will woo them. I won't take it as an affront or discrimination. It's just that they specifically need to know about one sector of the market. Business is a dull, practical thing.