It's even narrower than that.
The first three digits shoud be easy to guess if we know roughly how old he is and what state he was born in. If we had that info, I'll bet we could cut x down to 3 or 4 possibilities.
Actually, the first 5 digits can be determined based upon how old he is, and which state he was born in (assuming typical issuance at birth). The first three indicate the state (though some states have multiple triplets, which are rotated.) However, the next 2 digits are not random; they are used up in a set pattern, so it is possible to learn exactly what the first 5 digits were for any SS# issued in a given state in a given date range. Using the Freedom of Informatio Act, you can ask the governement the highest group number issued at any date! (http://www.ssa.gov/employer/highgroup.txt) Nice of them, huh?