Here’s what I don’t see answered: as a stepparent, especially a new one, you can’t be a savior without risking being too controlling. You have lots yet to learn in this relationship.
And successful engineering requires more than good math skills. It needs a mindset- my view is slanted but the questions are: is he a curious sort, does he get when it’s about bandying “ideas” and when it’s about the necessary precision and focus? Is he a tinkerer sort or he just thinks it would be “neat,” as so many kids do, to invent a better prosthetic leg, the next Apple phone or somehow save the world? Kind of like when many of us wanted to be astronauts or Indiana Jones.
By all means, work toward closeness. How you help him can’t be judged in advance and, I think, not always with “a plan,” other than to build the relationship.