Qualify university

If it is a public school, this rule does not apply to it. If the school is private, you may be eligible for a waiver or a tuition discount.
Also, a professor or former professor as a relative can help you to get admitted.

Sometimes university professors are enabled to provide tuition waivers for their close relatives.
If his children are too old for the college education, the waiver can be given to the grandchildren.
However, your grandfather should probably be still teaching to be able to do it.
In any case, ask the university about that.

Even if such offers exist in this university, they are made to the children, not the grandchildren of the professors.
Also, the professor should be currently working.
Grandfather won’t help you even if he’s working full-time at the moment.

I work at UC, and they offer only a nine-credit fee waiver for the direct relatives of the current employees.
Grandchildren do not count.
CSU provide a 50% discount, but only to first dependents, so you are not eligible.

First dependants may get something, but not grandchildren, and it seems he’s already retired.

No, it does not work for the retired faculty. If he is still employed, it may work for you.

Just call the university and ask.

Some colleges offer free or reduced tuition to the children of the faculty, but I have never heard about such propositions for grandchildren.