Is there a technical reference someone can point me to regarding an average lifespan of Eureka Lemon? UCR & Citrus Industry regarding Eureka's didn't touch on that.

From other sources, I've read the productive lifespan of such are 15-20 years, but of course can live much longer yet with limited fruit production.

Second question: My tree is 20 years old already. I assume the age would affect the quality of grafted scions of Mandarin and Sweet Oranges, also?
I plan to graft several different varieties onto it and years from now I'd be unhappy if I discover I should've just planted a new tree.

Thanks
Chris

For mandarins, generally the older the tree, the better the fruit. A 25 year old mandarin produces extra special fruit. A citrus tree can reach 100+ years of age. I know of a sour orange tree that was planted in the year 1200 (over 800 years ago) , that is still alive today, you can read about it in the book "The Citrus Industry". - Millet (592-)