Hi Edgar If he doesn't know any other languages it may be even easier to him. Everyone who learned Basic and wants to start with Haskell has to change his mind. That said the only reason not to learn Haskell is - there are existing solutions which work - you want to use existing Java / .net libraries - You want to target Flash or JavaScript only (or something like that) Nothing of that applies. I'd even say Haskell is nice for beginning because if something compiles it usually works (unless you hit advanced issues).
but I don't want to scare him away. Either he is scared or he is not. That won't depend on Haskell IMHO.
And mathematics, where to start? Ask him what he is interested in most. Start with that. Ask him what he wants to do .. If you have answers to that question Haskellers can help you easier and point you in the right direction.
Greetings Marc Weber