If he ever changes, it will be on his own. You can make people eat something once, but it won’t necessarily change him permanently. You can’t make someone more open to foods they don’t want to try any more than you could force them to appreciate music they don’t want to listen to, or wear clothes they don’t want to wear.
In past threads, picky eaters have been called selfish, spoiled, uncivilized, ungrateful, etc. As a still fairly picky eater, I would say it’s none of those things, but it’s difficult to describe to a nonpicky eater without coming across as picky and defensive.
I can’t say I’m more sensitive to flavors and tastes than anyone else; after all, I don’t own any taste buds other than my own. But I am very strongly turned off by certain flavors, textures, and aromas. Having them in my mouth makes me gag, literally. They aren’t foods I’ve had bad experiences with. I just don’t like them, and I’ve never been able to eat them.
Some eating habits are dictated by my knowledge of my body. For example, I tend to avoid milk and cream because it badly upsets my stomach. Ditto for spicy foods, for the same reason. The truth is, I want to eat that Cajun Alfredo sauce; I just know there will be hell to pay later if I do. But since I don’t explain my physiological reactions to foods every time I eat, I can see how others might infer pickiness from my menu choices.
And sometimes, foods just aren’t interesting to me, or I need to be in the mood to eat them. Why should I eat something simply for variety’s sake?
My boyfriend is a fascinating contrast. He’ll try anything, and his list of favorite foods is quite long. I envy this, and I wish I was like him. But as any dieter will agree, it’s challenging to change your eating habits, especially as people tend to be creatures of habit. You have to consciously seek out different things in order to experience different things. Most of the time, I will eschew variety and novel experience for the comfort of familiarity. And there’s nothing wrong with that.
Peer pressure is a non-factor. I’ve never seen my friends and co-workers pressure anyone into eating anything. I guess they have the class to drop trivial issues before they become arguments. My family hasn’t done it to me much either. If they did (and overdid it), I would tell them, as nicely as possible, that although I appreciated their concern and interest, they were crossing the line between concern and nagging. I’d ask if it was really worth ruining the meal over.
As long as your nephew is healthy and isn’t being a little bastard about accomodating his pickiness, this is not a problem, and it shouldn’t be treated like one. Maybe in a few years, he’ll start enjoying new foods. Or maybe he won’t. Either way, he has his preferences, and everyone else has theirs. The world won’t end just because they don’t match.