The indication was that this was a particular shop, not an overall company policy. Yes, it is not terribly frequent, but there are shops where the client is wanting the observations of folks in the particular demographic that is their intended audience.
So even though a grandmother might go into a store that sold a particular item for children, their target audience would be more likely to be those in the 20-40 age range purchasing for their own children.
A visit to evaluate a retirement home would be more likely to be done by someone of an age to be considering it for themselves or to place an elderly parent. And of course there are stores that I will self select not to request because I would stand out there like a sore thumb.
Tobacco and alcohol compliance shops have upper age limits to make certain that the customer is required to provide proof of age. Some types of bank or time share shops may need to have proof of a high credit score, just as some shops require proof of low credit score. During tax season there are shops where you need to be getting back at least a $1000 tax refund (and if it isn't that big, you don't get paid or reimbursed for having the tax return done). Some shops can only be done by males, while some can only be done by females. The potential list of exclusions/inclusions can go on and on. And then of course there are the requirements that you haven't shopped the location within a certain amount of time, or that your average shop score is at least a certain number, or that you go alone or that you go with someone.