What's the right age to start toilet training? How does it work for boys? Do you teach them to stand to pee or sit down first?

My nephew is 2 yrs old and is still in process of potty training. Unlike a few months before, now he has developed sufficient bladder control and informs us when he wants to pee. We make him stand in order to pee and luckily is not too pissed. He still does not like sitting on the pot because he has this feeling of falling and gets real cranky. We have a special seat for him but no luck yet. He just likes pooping in his diaper. The moment we put diaper on in the night, he poops :D Will try what diana lai has recommended above...