I need maturity help?

Ok so im 14 and people say im annoying and immature and i dont like it also my mother says i can do more stuff when im mature well i try but i cant always do it.... how can i be more mature. i also have a 4 year old little bro and he beats on me and i hateeee it but theres nothing i can do i try to be nice but he still hits me and my parents dont do anything cuse hes the "baby" can someone please help me (14yr old female)