This sentence is correct grammatically, and you could use it as an offence but it isn't a common saying at all. Something a bit more common could be 'You have a small/weak mind/brain' (When used offensively, brain and mind is generally seen as the same thing)

You could say 'Your mind is finite,' but if you mean to be offensive or insulting these work better: You are stupid. You are dumb. You are ignorant. They are pretty much mean the same thing.