Hi C.---I think I would make sure that he is washing under his arms properly, first. Soap should take care of the bacteria that cause odors.
If using a deodorant, be sure to use one that doesn't have aluminum in it. That is used primaarily as an antiperspirant, but excess aluminum in the body is seen in alzheimers patients and is also thought to be a potential problem for breast cancer.
I just 'googled' body deodorant remedies and this website came up, http://www.home-remedies-for-you.com/remedy/Body-odor.html. There is also a suggestion on foods to help prevent body odor. It's funny, I am a wellness educator and I give talks on the importance of good nutrition for good health and disease prevention. Of course it makes sense that a good diet would help the body to minimize bacterial growth, even on the surface of the skin. If you would like more information on how diet and lifestyle impact our health, please feel free to contact me.
In health, D. ###-###-####