Agreed with mom2collegekids - he shouldn't be thinking about grad school unless he knows what he wants. The high attrition rate in grad programs (esp. PhD ones) is largely attributable to the students' reasons for entering the programs in the first place: usually they think they have to in order to make money, or to have a good career, etc. He needs to soul-search and find what his 'calling' is - it might not require grad school.
On top of that, the best grad programs are legitimately more competitive than HYPS for undergrad. Their acceptance rates routinely hover at or below 5%, esp. in STEM fields. Of course, many more have higher acceptance rates, but keep in mind that grad programs attract more international applicants than undergrad does, and grad programs in general are more willing to accept internationals (often 1/3 or 1/2 or more than half in a given program are from abroad). So applicants are very much competing against students from around the world.