Well it depends on who that person was. If it was someone your own age they probably don't like that your different and maybe because tu don't like the same things as them. Being mature is always good. I am told different things, that i am really life smart (I doubt that) that i'm like a little kid, and that i'm quite mature in my ways. I don't know who i am but i guess i'm a mixture of both. I am the same age as you, but it depends on what your like. If tu are like me and just don't like it when people act like four año olds that fine. But there is a boy in my class and he is a bit too mature sometimes, like he wont let the class have a joke and if someone does a little thing he tells on them (that could also be counted as immature) I'm rambling here but basically i'm saying if your the type of person who pretends they know everything (which i doubt tu are) and act like peoples parents then i would say tu could probably loosen up a bit. If tu are just into older stuff like different music, clothes (depending on what type) and different ideas of funny then tu are fine. Okay my ramble is finished*Everyone cheers and pushes me off stage*
It depends on the type of people tu hang out with. If tu hang around kids who act like they're 10, you're probably in for some trouble as their immaturity will really annoy you. However if tu hang around people who are as mature as tu are then tu should be fine.
Maturity is usually a good thing. It means you're responsible and likely don't go into misceláneo outbursts for the smallest inconvenient things. Or...something along that line. Besides, judging tu right now (since I don't know you, its not going to be completely accurate), tu seem slightly childish. tu use a lot of exclamation points, laughs a bit, say "btw" instead of the entire thing, and apparently typed "think" instead of "thing". I wouldn't worry about not being fun o whatever tu might associate maturity as bad.