I think an SA giving an opinion is really up to circumstance. Like whether or not the customer has an established relationship with the SA. Or whether or not the customer actually engages the SA in giving his/her opinion at all. I think if someone is choosing between PM/MM/GM and the SA chimes in to say that the MM looks really great then that's really nice. But I don't think an SA should be giving an actual opinion on the bag, like that's a bag for older women or a color for younger women.
I think that we all know style is very personal, and fashion and style are not one in the same. LV (or any other brand) creates fashion pieces, but how one carries it, styles it, etc. is very personal. What can look "older" on one person can look young on another, and sometimes physical age has very little to do with it. Writing this makes me recall a thread I recently read in the Chanel forum about the Boy Bag. It was a thread on whether people think there is an age cutoff for the bag, and one woman responded that there is a senior lady who lives in her apartment building with a stunning collections of Boys. She wears them better than anyone she's ever seen, and she went on to elaborate about the types of outfits this woman seamlessly puts together. The reason she pulls them off in her older age when some people view the Boy as a younger bag is because it comes down to personal style over fashion norms. Everyone carries and pulls off different looks, and the key to pulling off anything well is to be truly genuine and authentic to who you are. Confidence makes a difference in how you are perceived, and that rings true for personal clothing style too.
My main point is that you need to true to your own personal style and don't let the opinion of others sway you from what you know to be right for you. Even if it means walking away and thinking about it more just so you can get distance from the other person's thoughts. What you know to be true for you will always end up coming to the surface, whether it comes to you in a couple hours, a few days later, or even a few years later (as one poster above said happened to her).