There is a code on your tyres that tells you how old they are, it is a four digit code first two are the week of the year, second two are the year of manufacture, located close to the wheel rim and only on one side of the tyre, aperently it is ileagal to repair a tyre over four or five years old not sure exactly how old.

if anyone needs tyres I can help as my brother sells tyres on his farm ( next to mine ) not far out of Manangatang in Vic caries a fair range of car and trailer tyres up to truck tyres 

PM me if you need help in our neck of the woods 

Woody