If he’s eligible for parole at 1/3 of a 25 year sentence, he will spend anywhere from between 8 years, 4 months in prison or 25 years. That would make him somewhere between 40 and 57 when he gets out.
He is not; there is no federal parole (for people sentenced ib the last ~37 years.) There is “good conduct time” that can reduce time served to not less than ~85% of the time sentenced, so around 21 years minimum.
SBF was sentenced somewhat after 1987, so those rules don't apply to him.