The age appropriateness of these brands refers to the cost. (and some of these houses aren't worth the money even when one can afford them - but each person has his favorites and his dislikes). Many of these brands should be off limits at your stage. The reason is also that you shouldn't rush into buying something very expensive before your tastes have settled and you have experience. Something that may smell great at the beginning of your journey may turn out to be not as good when you smell other things.
I think you could focus on brands that offer 50ml bottles for about $90, which is more or less the entry point for niche. These include Diptyque, Artisan parfumeur, and my very own favorite Etat Libre d'orange (they also have a sampling set with all of their perfumes, some of which are really excellent). CDG also is around these prices (though I don't know if they have a sampling program), CDG2 man being probably their best known. Lutens would probably the most famous niche house, though again I don't think they have a sampling program.
You should also try to make the most of trips to big cities and places that carry these brands. For instance, Creed and Bond are quite ubiquitous in the States, so much that one wonders whether they ought to be called niche.