I'm not a big expert on body armor or armored vests but to my understanding, some vests like the Kelvar type wear out after 5-6 years. These vests may lower the quality of protection or become useless.
I wouldn't buy a body armor vest that was 12 years old.
There are a few brands & types of material available on the US market.
For uniformed security or extra protection, you may want to buy a over-garment with body armor/plate inserts. I've seen a few firms that market uniform vests/garments(black, green, white, navy blue) that could work with your regular security shirt.
For details about good body armor choices & related products; cases, hangers, garments, IV/plates, etc see; www.galls.com www.policehq.com www.uscav.com www.actiongear.com www.qmuniforms.com
Some online retail sources/firms require security licenses or LE status before buying. Your military/MP identification may help but check with the company before you order.
I'd look at the Second Chance line in class III or the IIA with plate inserts(chest-back).
ps; top body armor isnt cheap but it's far better than used or out-dated equipment.