I usually go off the manufacturing date stamp on the inside of the helmet. The helmet in question states it was made in March of 05(it had set on a shelf at the LBS for a couple of years). Given snell's advice of replacing every 5 years and the manufacturer's of every 2, I usually shoot for 3-5. So, it about due for one.
I usually cut the straps out of one I throw away, especially the crashed ones