I had the same idea with you to train him as PF but an other  experienced person (he is in Nt team) said me to train him first outside skills until 21...My point is to get as much money as i can when i will sell him so his idea sounds attractive
Both ideas for this player is right...depends on in which position you want him to be more useful and in which categories..
This   player    can be   perfect   for   a   PF,you   can  train    his   OD  first   to   8,then   IS  and  later  ID.
When    that   is   done    just  train   rebounds/ some JS  and   you  will   have    a  multiskilled   PF.
SF    will   take   way  too  long and he  is   almost   20/ and his  height,you   need    13/14   OD  and   11/12 ID.
To  train   a   SF   ,you   need    a  trainee   who   has    a   complete   skillset,because  training   a  SF   is   a  very   long   road..