I was diagnosed when I was 2 years old and am now 32. I've been in and out of remission for the last three decades, and though I do have bad 3-4 month periods with increased edema and proteinuria and the necessary medications (Prednisone, Furosemide, and now Cyclosporine) I haven't had too many difficulties with my regular day to day.
Diet and excersice help tremendously in that it helps combat the malaise brought on by the edema and weight gain from being on steriods. Low sodium (I'm sure you've heard this) and keeping active helps reduce lethargia. And that can go a long way.
I'm in a relapse now, which is why I was searching online for information, tips and tricks, and to read the support system, but I've had the experience and confidence to know that I will be in remission in few months. Hang in there. Advise your son that there is just this one bit of him that he can't control, but he could do much to prevent the ill feeling that arrives when he does relapse.