The Level Above Mine
Eliezer, don't think to yourself that you only have until you are 40. As somebody else noted and you didn't acknowledge, Marcello was not yet born when Conway passed 40. You mentioned your father, and I don't know the specifics, but surely you know that plenty of people have done great work, sometimes their best, past 40, and that with every passing year, due to advances in health, medicine, etc., "youth" extends further and further into our life.
And as another poster mentioned, I have almost no doubt that Von Neumann would have blown Einstein (possibly Godel) out of the water in terms of ability, and at the age of 10 or 11, William James Sidis would have smoked them all (at comparable ages). Even if there is such a thing as general intelligence and even if one has less of it than somebody else, it is still very much possible that one is vastly more talented in particular areas.
Einstein probably didn't have an IQ in the realm of Von Neumann or Newton or Sidis, but what he did have was an incredible physical intuition and the ability to think deeply about the philosophical underpinnings of physics in a way that few others could (or can). As others have said, even if Conway actually is smarter (which you should not just blindly accept, because we all have cognitive biases that might prevent us from making an accurate judgment), it doesn't mean that you don't have profound gifts that will end up being the deciding factor in solving FAI or whatever else you set your mind to.
Looking at Von Neumann at age 24 and Einstein at age 24, NOBODY would have thought it remotely possible that Einstein would be the one who would achieve enough in his field to be considered a successor to Newton. Von Neumann, though he accomplished more than 100 "mere" geniuses could ever hope to accomplish, cannot be said to be a successor to (or in the same league as) a Gauss or somebody of similar stature.
Since you're so fond of quotes, here's one for you:
If you can solve your problem, then what is the need of worrying? If you cannot solve it, then what is the use of worrying?
- Shantideva (Indian Buddhist philosopher)
Just get on with it. Self-doubt and endless self-analysis do not contribute to the end goal.