What prompted Pharaoh to ask Yaakov's age?
Ramban, Hadar Zekenim and Rashbam: Because Yaakov looked way beyond his hundred and thirty years. 1
Moshav Zekenim #1: Yaakov said that if Pharaoh will let him return to his origin after the famine ends, fine. If not, I will return [now] and buy from Yosef. Pharaoh asked, at your age, do you expect to live so long - how old are you?
Moshav Zekenim #2 (to 47:10): In Pharaoh's youth, he went to Avimelech to learn Derech Eretz, and saw Yitzchak. He now thought that Yaakov is Yitzchak, and was astounded that he is still alive.
In the days of the Avos, the life-span had already been cut short and, except for Tzadikim, people died at the age of 70 or 80 (See Ramban to 5:4), like it says in Tehilim 90:10.
