His mental age is less than physical age

I understand the concern towards your brother. However it is unclear what you mean by saying his mental age is less. From the information provided your brother seems to be suffering from anger dyscontrol, may be due to his personality traits or even adhd. More clarity is needed regarding his problem to decide on severity of the condition. It is manageable with appropriate treatment, so that dysfunction due to the same can be reduced and his quality of life will improve. Some counselling sessions and if needed medical help might be useful for him. I would also be more than happy to help you with that if you are looking for further online assistance. Discussions will be held confidential. You can directly consult with me through Practo as needed. Online chat consultation is available.