I can sort of relate to your brother, though I genuinely don't have the capacity to show appreciation because most of my childhood has left me with mental scars that resulted from neglect from a certain step-parent who didn't (and still doesn't) look after my interests and sees all the negatives in me and expects me to be the big brother (being the eldest sibling) and take such responsibilities such as supporting younger siblings / parents with rent and so on. The only thing I can think of to my defense would be I have a simpler mind, and it hasn't fully developed into an adults quite yet.
So, i'm not sure if your brother is on the spectrum himself - if he is, i'd exercise some restraint because he may not be aware of what impact it's having on you.
Strange enough at 25 I feel like i'm still a teenager because I really do get treated like one: no job, holed up in bedroom, everything handed to you for free. But at the same time they are reluctant to help me because either they realise i'm a lost cause or they see i'm old enough to make my own decisions.