What is the age limit of heart bypass surgery?

None, but...: Early 90 's occur, but late 90's (or 100s) are rare.

There is no set age : However, as with any medical procedure, one must weight out the risks/benefit ration. As one gets on in age, the risks of undergoing this procedure increase, perhaps to the point where the risk of death outweighs any potential benefit. The doctor and patient must then explore all possible options. Also remember, some 80 year olds are healthier than others.