I've only ever had an issue with Pirelli car tyres that were over 5 years old when 'new', the sidewalls started cracking within the first year. In '81 we bought a '58 NSU scooter, it still had the original tyres, I rode on those tyres until I sold it in '94. My current 2012 PCX150 has covered just over 6,000kms, the scooter is garaged, the tyres are probably only a 1/4 worn and there is no visible damage. Throwing tyres out at 2 years may be a little excessive, in my case they will have covered no more than 2,500kms.I always check to make sure the tire is less than 2 yrs old at the most. The older tires tend to come on sale, so watch out.