In my case I actually find adults easier to talk to than my peers. Usually any conversation I have is not a one way conversation. I learn from the elder person and visa versa.
I would find it offensive if I was 21 and people thought I lacked the maturity to hear certain words. I don't know the exact reason why people would hide it from you but if you are brought up in that type of environment the that's how it is. Of course, this will change in the future, but you may have to put up with it. If it was me then I would try my best to prove my maturity and gain respect from the community.
As long as you know where you stand then you shall be fine. It shouldn't matter what other think of your maturity. They are in the wrong if they wrongly judge it. I do, though, feel for you being in that situation. Do what you think is the best action to take. Prove through your faith to others that you are wise and not child like. That is the best advise I can give.