due to the time travel issues it is possible that Jacob is not an older member of the island society. he could possibly come from anytime as long as aging on the island is possible even if you are not from that original time period.
-we saw that Faraday is comfortable with the idea of time travel threw his experiments at Oxford. he pretty much figured out, with the help of Desmond how to send a rats mind into the future to learn something it had not learned until the next day.
-Faradays equation that he was working on was off and needed the set of numbers that Desmond gave him. either way they completed the equation and it was important in the year 1996.
-when time was still, most ended up in the 70's. with the knowledge of having that equation from the future could be very beneficial to the experiments with the controlled time travel that DHARMA was trying to achieve.
-this knowledge could have helped him get in close with Chang and prove his worth. it is possible that with what he knows and what the island is, that he him self has been traveling threw time ever sense they began to work together.
-this could be for any number of reasons. but in conclusion; if Faraday, for any reason had the privilege to travel threw time (mind or body) he would have information from the past and future. thus being able to make decisions on things that need to be changed or set in place in the present for any number of reasons.
in closing it is Friday and i am at work. this made alto more sense in my head. but it was an off week for lost so i may be just trying to create drama in my head to fill the void. also bc this is an awful attempt at a theory i must make it clear that i am a much better lost fan than this post depicts.