Seems very unlikely that he's got Marfan's. There are of course exceptions, but other problems that go with the disease generally do not go hand in hand with being a great athlete. Often those that are athletes and are undiagnosed suffer sudden death from a ruptured aorta! Anyway, beyond the long arms and large hands he doesn't seem to have most of the signs.

Certainly unless you could pull out all of the undesirable traits, I doubt you wouldn't want to actually genetically engineer anyone to have Marfan's ..... people with it are prone to retinal detachment, spinal problems, lung dysfunction, aortic dissection...