The reason your PC took dragon at 1st level is not because he wants to face a bunch of dragons now. Its because the favored enemy bonuses get better with levels. At high level, he wants the best favored enemy bonuses against stuff he'll face at that level-- like dragons, or evil outsiders, etc.
Taking goblins as your favored enemy at 1st level might make sense in the sense that a 1st level character might likely face a goblin, but in the long run, is stupid, because at 20th level his best favored enemy stuff will be against a creature he does not need it against [he could kill a goblin with his eyes closed] and would almost never be facing anyway. Whereas against a dragon, he could need it.
So don't feel bad about not having dragon encounters for him-- he does not want them now. he is just getting prepared for them later.