By the time we reach this Parsha Avraham is an old man. Despite his chronological age, he showed no outward physical signs of aging. In fact, according to tradition, no one at this stage of the world showed outward signs of aging. They remained youthful and healthy until the moment of their death. Since Avraham's father looked similar to Avraham, it was very hard to determine who was older. This presented problems, for example, for those who wished to honor the elderly. According to the Midrash, Avraham asked Hashem to allow people to age externally. Hashem honored Avraham's request, and from that point on, starting with Avraham, people started to show signs of aging.
In Tanach, four factors that cause a man to age are identified: fear, aggravation about children, a bad spouse, and war. In דברי הימים ב' (א:ל), it says that David aged due to fear: "He was terrified because of the sword of the angel of Hashem." This is clarified when it subsequently says, "and David was old." In שמואל א' (ב:כב), it is written "and Eli was very old and heard all that his sons did to Israel." He became old on account of the aggravation that his children caused him. Regarding Shlomo Hamelech it says in מלכים א' (י:ד) that his wives served idols in his old age and he failed to protest. These idol worshipping wives caused Shlomo to become old. Finally, Sefer Yehoshua (ד:כד) states that Yehoshua waged war against thirty one kings and immediately afterwards it says that Yehoshua was old.
In contrast, Avraham did not fit into any of these categories. He had assurance from Hashem of protection, his wife was great, his sons followed in his ways, and he is blessed with good fortune in this world. Avraham's aging was a crown of glory and honor.