It is a green Fatgue shirt from the 50's to late 60's. The sleeves have no cuffs and buttons, which came out in the 70's. The person was probably in the 1st Cav, but liked the motto of the 2d Armored Div. There is no name tape or US ARMY tape sewn above the chest pockets, and to have the his first name and GTO embroidered on the shirt, means it wasn't worn on active duty.
Semper Fidelis,
"Huey Bubba & Co-bro"