3 1/2 yr old gags on potty

My friends 3 1/2 year old son will not potty train. But not for the "usual" reasons. When put on the potty he gags and sometimes even vomits from his disgust of the pee and poo. She started at approx. 2 1/2 years on a potty chair and has him on a regular toilet sometimes with a potty aid now. To add to the difficulty he is a large boy with a small penis. He is not able to aim it into the toilet while standing and definitely not while sitting. Please offer advice. Thanks

[Kevin Kennedy, Ph.D.]

Relative to the latter point, the guard on the potty will be useful. Relative to the second point, all that can be done is to be patient and supportive. If there is an older sibling, that sibling can serve as a model.