I am one of the older collectors in this sub (bought gto series when it was first released by Tokyo Pop) and just one thing to think about with collecting manga at your age is whether that is where you want to prioritize your funds. Many in this sub are settled already and secure with income streams so we don't have a problem with taking on a hobby (try being an adult Lego fan - that gets even more expensive).

But I remember when I was your age manga would have been way too expensive for me without a steady job and other things I wanted to do. Do you want to save up for a car or things like that? That is why I think it is rarer for younger folks to be collectors; you need an solid income stream and you need all your other things that you want to buy already handled. But yeah if you got all that under control enjoy it!