this is just my opinion but A quality helmet sitting in a box for a little while should be perfectly fine. I'll buy a year or 2 old helmet anytime if i can find a deal on one. If the helmet was strictly for street use i'd even buy a 3-4 yea old helmet however track days and racing requires it cannot be more then 5 years old

However I believe they could be worn out after a few years of regular use.