Marianne is only sixteen. At that age a very few years appears to make a huge difference. I recall that when I was that age women in their mid-twenties seemed to belong to an entirely different generation.

Add to the blinkered perspective of youth Marianne's reluctance to apply reason and her conviction that feelings and emotion are all that matter. Women in their mid-twenties were either married with the responsibilities of a family, or "on the shelf", and in any case had calmed down somewhat from their adolescent selves and were probably less given to florid displays of their Sensibility. To Marianne they were obviously "over the hill".