Solidus actually looks a lot like Big Boss--even more than Solid or Liquid do, particularly because of his aged features. It can't be Solidus in Snake Eater, though, because he was created in the '70s, just like the other two Enfants Terribles. Ironically, the reason he looks older than Solid and Liquid is because he was created after they were, meaning Big Boss's genes were that much older at the time of cloning, so the clone's aging process was made that much more accelerated.