I'd imagine the older ones get a slight advantage at the beginning, as 10 months to a 4-year old is a lot more significant in terms of development, but less so after a year or two, when everyone will have reached the same plateu.
However, starting younger could also mean you have a better chance, as you get into the habit of learning things regularly earlier on, so the pattern is more established in your mind as it comes earlier in your development. I'd imagine that this effect is limited somewhat though by the disadvantages in confidence, social skills, likelihood of having played with other children and physical stature that the situation would also likely entail.
I was born in July, and I'm at least as intelligent as a 9-year old born in September. Some of my best friends are black, too.