Fruiting Lifespan of Pear on Quince?

Years ago I put in several pears on dwarf rootstock to get the ball rolling while I waited on the big ones. Plan was to get rid of them later, but now I am wondering how many years of actual fruiting I can get out of them. Anyone know what the fruiting lifespan of pear on quince or other dwarfing rootstocks is? How old is yours?