My grandfather is 80 years old. Is it safe for him to get his AAA repaired through endovascular surgery?

Yes. An endovascular repair of his AAA will be much less traumatic to his body than an open repair. Nothing we do in medicine is without risk. Assuming he has a large aaa, the risk of endovascular repair will be less then the risk of watching and waiting (doing nothing).
Safe? Yes. The operation can be tolerated by almost everyone regardless of age. Whether or not he'll benefit from the repair depends on the aaa's location, size, and shape, and his life expectancy. Talk with a vascular surgeon or two who can help him make this decision.
80 year old repair? Absolutely, if he has been evaluated and has the right anatomy for repair his age alone should not exclude him.
AAA. It depends on his overall condition and cardiopulmonary risk. The repair is more well tolerated in the elderly than open surgery but still requires anesthetic.