And I don't think it's true either -- that older people are the major buyers of premium groceries. I don't see that many older people when I go into premium grocery stores -- except if by that you mean 35-50.
Upper-middle class foodies. Who are probably less likely to be women than the market for non-premium balsamic.
http://www.nielsen.com/us/en/newswire/2011/in-u-s-men-are-sh...
...which suggest that men make 38% of retail grocery shopping trips. So, if you're going to envision a representative person who is looking for a grocery item, you should probably start out by envisioning a woman.
It is, unsurprisingly, difficult to find more specific information online for free. Instead, by googling "market analysis salad dressing", I find approximately six market research organizations that offer to sell me a report. Perhaps the OP has bought such a thing, but none of the rest of us are likely to bother.
Of course, what actually matters when trying to convert website visitors is not the demographics of the universe, or of US grocery buyers, or even of US buyers of balsamic vinegar, but the behavior of the people who are actually reaching the website. About whom we really know nothing.
It doesn't have to represent the 100% of the consumers of such products. Just the majority.
And by the unwritten rules of how we talk about such things (in essays and such), they don't even have to be "moms of the PTA" literally. It's enough to be "moms of the PTA"-like, ie. ascribing to belong (and exhibit) the same kind of social characteristics (class, sophistication, etc) as "moms of the PTA".
