Ha ha, it's not your age, IB stands for International Baccalaureate (IB). It is just like, if their school systems ever had, Honors for high school or private schools. IB is a highly regarded thing for colleges, if they accept it. They love to see it on your records. It is a lot of, but if the college you want to go to accepts it, it will encourage the college to accept you big time. About 10% of the people who join drop-out though so be warned, it isn't a breeze. You might need to give your son a tutor if he never took pre-IB or the IB classes prior, because for ex, in geometry or trig, regular would have an 8-step problem to solve. IB courses might require you to do a 10-15 step problem of a like matter. When my son took it, the college was very interested in it, but he took it from 9-12 grade (9+10 were pre-IB, 11+12 were IB). I'm not sure if he can still join IB if he is a senior, because most places require it taken in 11-12. But thats all there really is too it. IF you want to learn more here is the link to the site that hosts it:
http://www.ibo.org/