Do you think I should tell my parents my little brother will never get better
Is there a reason telling your parents that?
Yes, because that kid is slow-minded
You shouldn't think so poorly about your own brother. You should be more supportive of him.
That kid just ends up slowing me down and it's really annoying me.
It sounds like he's younger than you, so he has a good reason to be slower. Try thinking realistically about your capabilities at his age. Would you have wanted the older kids judging you like this?