Here is a link to tell your tires age:
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=11&s_kwcid=AL!3756!3!50154916573!p!!g!!tire%20age&ef_id=U1dY8wAAAR5fh@L3:20150303222917:s
Maybe Ned can fix that, I've tried to shorten the links but believe I had a technological bypass at birth, because I've been unable to make those cool links that say ; "click here"
And here's a link to a story about trying to legislate aged tires off the road. http://abcnews.go.com/Blotter/tire-industry-fighting-legislation-aged-tires-off-road/story?id=23686666
In it Michelin says 10 years it their limit, while the industry recommendation is 6 years, others will say 7 years.
For myself I keep my tires covered, when not in use so they are out of the UV rays. But inspection is key, if they look dry rotted with cracks in the sidewalls, I'll replace them at 3 years. If they continue to look good, and don't lose more than about 2 lbs of pressure a month, I'll stick closer to the 7 year mark. But if you've ever seen what a failed tire can do to a MH or trailer, you will want to get those tires replaced before they blow. A friend of mine had a tire blow, and the wheel well of his unit was only plywood, which it shredded puncturing the interior. It cost him over $4,000 to get all the repairs done. I'd be interested in what the most damage done by a failed tire is, but I would thing $4k is pretty close to the top, but it still would pay for a full set of tires.