The size tag is VERY worn. I think I can barely make out that it's a large, and I can't imagine why he would have gotten a larger size, but
check out the measurements below to make sue it'll be a good fit for you.
Measurements, laid flat and not stretched:
Shoulders (between tops of shoulder seams) 20 inches
Chest (pit to pit) 21 inches
Bottom opening 21 inches
Length (from top of collar in back, to bottom) 25.5 inches
Sleeve length (along top, from shoulder seam) 7.25 inches
Material: 100% cotton
Let me know if you have any questions!