Two thoughts.
1. Having played college and then Men's Club rugby, if there was a 40-50yo guy out there still playing, it was usually a Prop, which most closely resemble an OL. Can't explain why, but it was almost always the case.
2. He's playing for North Dakota State School of Science which competes in the National Junior College Athletic Association, so he's not competing against athletic 260lb+ DL.
I'm sure he's more sore than the 19yos on Sunday, but this doesn't seem that crazy to me.