
It's best to have these things on hand when you have formal events. I have a 17 neck son but doesn't need a huge shirt so these extenders may help.

Gildan Performance Men's π Clothing and Shirts with Moisture-Wicking Polyester
44 Review

H2H Mens Casual Slim Fit Short Sleeve T-Shirts Cotton Blended Soft Lightweight V-Neck/Crew-Neck
46 Review

Men'S Long Sleeve Polo Shirt - Slim Fit, Stretchy, Breathable Collar
43 Review

INFLATION Bamboo Shirts Sleeve Elastic Men's Clothing in Shirts
45 Review