my sister - she was 2.5 years younger She started out quite smart but with an age disadvantage, but then quite early developed some sort of life-long emotional resistance to memory and learning.
I don't believe it's taking advantage of someone who is stupid. Stupidity implies that they are resistant to learning as opposed to someone who's ignorant and has not learned.
I would not consider that example "unfair". And I think it all gets down to what is considered "fait" or not. Many people have certain advantages but as that is natural I cannot see that as unfair. Here at work many people believe I receive preferential treatment but I have been here 29 years and the higher ups know and trust me. I don't think it should be seen as , for instance, a race we have to run daily. Some people are naturally thought of better than others which might be unfair but is very real.