Cool that you're trying to help him. Art training can greatly help, although it's more like opening your eyes and mindset for creativity instead of perfecting the "basics" (drawing, modelling, sketching, ...). At least, that is what I know from friends who did art academy.

Someone with talent can learn this him/herself, if the motivation is really there. Your nephew seems to have that talent, now it's a matter of making good use of it and finding out where's his real interests are. Having something that he loves can greatly improve the motivation. Being a skilled artist is talent + LOTS of practicing after all.

Most people don't learn drawing because they simply don't know what to draw, so there is no motivation. I can draw pretty good myself, but only a few times a year (making Steven Seagall, Sadam Hussain or Paul Teutel portraits as birthday presents for friends). So I'll never reach the state of a real pro. But if you two can find something where the heart is... Some people love comics, others go out on the bike and pick a spot to draw a landscape. Yet another person is into technique or sci-fi and uses that as a platform for its creativity. People here ussually love to draw/model game maps, monsters, characters or animations. It could be anything. Try to find that out, then focus on it with the pencil, clay, glue&sciccors or computer programs.

If that works out, you could try to shape it into a (small) project. Things are extra fun if you can make practical use of it. For example, make a big wall painting in your bedroom. Create a series of things to decorate your house. Write a story with pictures. Make wedding cards for a family member. Join a game MOD/offer help to a game project. Or something I always liked, build a miniature city :)


Good luck, and again, good thing that you're helping! Many talent is wasted unfortunately.