I think you really try to be certain you understand what your son's production flow might be like.
There are a lot of people around at the moment (including my stepson, for example) who are very, very focused on a musical style that in turn is built around a production style that is really only well supported by Ableton Live (although the most recent versions of some other major DAWs including ProTools get close in many ways).
If that is how he imagines making music (samples, beats, looping, slicing, dicing, triggering, pitch-shifting, tempo-fitting) then giving him more traditional tools (particularly Ardour or Mixbus) will probably prove rather frustrating. On the other hand, if he actually plans to record himself or others playing instruments and then edit and mix the results, then Mixbus could be a deeply satisfying option. And note: it isn't that you can't do the Live-style of production with Mixbus (or Ardour), but it definitely doesn't flow in the same way.
I know the music my stepson makes, and he has mostly used garageband on his mac (despite living in the same house as me!) But he finds that pretty frustrating and really wants to get into Live as his next tool.