To answer you questions:
is it really possible to be too young for a perfume?: if you mean the extrait or the highest concentration of the scent, i'd say that if you're 19 you're not too young to be using that, and i would recommend you to use whatever is it that you like best and not what pleases others.
is a perfume too classy, bold or old for someone your age? : no, if you like it and it feels comfortable then it's ok.
and for the last one, i don't think it's inappropriate to find a signature scent and to use it on all seasons, it's a personal choice and it complements who you already are.
I would recommend Le Dix by Balenciaga and Guerlain's Parure to try out, there's so many out there that it's really a personal quest to find what you really like.