Do RE-71RS Tires Age Out?

I have a set of RE-71RS tires that have been used for the last two seasons for autocrossing, and some street driving (like to and from the autocrosses). They are on my 2010 Cayman S. The tires probably only have 16 autocrosses on them (4 runs per auto-X, so 64 heat cycles), and are worn down to between 5/32" and 4/32". Not a lot of heat cycling on them, and they've never gotten really hot, like at a track day (which I sadly have not done lately). Lots of tread left, but the tires being two seasons old has me wondering if I should buy a new set. When not in use I store them in my garage out of the weather and sun. I'd prefer to save the $1200 - $1300 new ones cost, but I am also a pretty competitive person around motorsports. 

What is the wisdom on the shelf life of RE-71RS tires?

All tires age out, I'm sure they're not as sticky as new anymore so if you really need peak grip you could sell these and put that money towards a new set. For a person who wouldn't mind losing a position or two due to not having the stickiest tires they'd be fine.

You're referring strictly to a drop-off in performance due to a couple of years' age, and not the tires' expiration date? I wouldn't worry about them being unsafe. If you're trying to be competitive nationally, then you would probably be best off buying new tires every season (or more frequently). Where are you on that scale? 16 events' worth of heat cycles at autocross events probably didn't make them better than they were when they were new, but if you're just trying to beat your buddies out on the autocross course, they're probably no worse this coming year than they were at the end of last year's event.

They are junk.  In order to help you out, I'll take them for shipping cost so they are out of your way!

Realistically, I haven't seen them fall off from that low number of heat cycles.  I'd keep on pushing them.

In my experience 16 autocross heat cycles is at least getting pretty close to dead, but my heat cycles are probably a bit more aggressive than most and the tires are usually just into the wear bars when they start to go off (I don't really track heat cycles specifically but it's been around 130 runs plus a fair amount of street driving, at 6-8 runs/event that's around 16 events). Basically you'll know if they're still good or not from driving them. Two years of age alone should be a pretty minimal impact as long as they've been stored reasonably well.