This is more on the technical side, but he might be interested in using Adventuron - I haven’t personally worked with it but it bills itself as easy to use in terms of creating graphical text adventures.
If he’s worried about his lack of coding skills holding him back I’d point him towards CodeAcademy - in particular their free Javascript lessons are useful if he wants to keep noodling around with Twine. A little knowledge goes a long way, here - you really only need a little programming knowledge to be comfortable with Twine, and knowing the basics of programming will give him the footing to learn other creation tools if he wants to.
Finally, I find Emily Short’s Idea to Implementation extremely useful in how to lay out a game start to finish without falling into a number of common pitfalls.