Really at wit’s end to answer your question. My neck size (dress
shirt) is 18 1/2 inches; so a necklace that is that or shorter will
not even go around my neck. So I guess, the first thought is that
you need to know your nephew’s neck size. Then I would add 2 to 4
inches at least for the necklace to be comfortable.
John Atwell Rasmussen, Ph.D.
Geologist and Gemologist
Rasmussen Gems and Jewelry