I agree to wearing what pleases you, when it pleases you. Sometimes, I'm in a mood and wear Blue Amber on a summer day with jeans and a white T-Shirt---but not usually.
I have never worn kai in December with a chunky sweater and corduroys, and I never will. I will take a stand right here: it would be wrong.
I notice the replies were from all men, and I think women's fragrance has a somewhat greater seasonality and day/evening split. You don't find too many men's fragrances that are fresh, transparent, green florals. I save them for summer, with the odd day of winter rebellion.
At the same time, I don't think I wore Chinatown all summer. Something about the rich amber/vanillas can be choking when I have sweat trickling down between my shoulder blades. I don't tend to reach for incense fragrances in the summer heat--or in spring, either.
IMO above the age of sixteen, age doesn't matter. I don't think I'd care to see a young girl wearing something really sexy, but what is "sexy" is a matter of opinion. To me, that would include most spicy, vanilla, patchouli, ambers.
That said, I think a young woman should have a white musk, a vanilla, and a light fruity floral. I also think she could have anything else she wanted, but these would be a versatile trio. Perhaps now I've bumped up this thread, some of our other women will weigh in with their opinions!