Maybe he's younger in this Alternate Reality. Maybe this isn't 2009. Maybe humans here last longer. It doesn't have to make sense, they can do whatever the heck they want with this and have a reasonable explanation within the show... can't limit ourselves to what we know as truth in our world. Heck, we have Observers populating what I assume is another Alternate Reality.
Well..ok. There are all kinds of paradox here but there are also some hints
First, there is the idea, as the observer says, that there are "two of everything"
So the second Peter is the second Peter, the twin towers are the second twin towers, the John F Kennedy, the second John F Kennedy, etc....
They are all remarkably similar. The Len Bias thing doesn't make sense because he can't be the same Len Bias. Assuming there are near exact replicas, which is not a bad assumption at this point, the earliest Obama could be president is 1996 (I believe), so at that point Bias would be a 10 yr vet...so I guess if its another time its possible..
But it just doesn't jive to me. There are other things they could have said...something like "Sox Choke again, Curse of the Bambino going strong at 91 years" or something.