age - How old was Eisav when he fell into bad ways?

Rashi on Bereishis 25:30 states that Hashem shortened Avraham's life by 5 years (180->175) in order that he shouldn't see Eisav, his grandson acting wickedly ('Tarbut Ra-ah').

And on that day, Abraham died, lest he see Esau, his grandson, falling into bad ways, for that would not be the “good old age” that the Holy One, blessed be He, had promised him. Therefore, the Holy One, blessed be He, shortened his life by five years, for Isaac lived one hundred and eighty years, and this one (Abraham) [lived] one hundred and seventy-five years

However, Rashi states on Bereishis 25:27 states that from the age of 13 it was clear that Eisav went into bad ways

And the youths grew up, and Esau was: As long as they were small, they were not recognizable through their deeds, and no one scrutinized them to determine their characters. As soon as they became thirteen years **old, this one parted to the houses of study, and that one parted to idol worship. — [From Gen. Rabbah 63:10; Tanchuma, Ki Theze 4]

So how old were Yaakov and Eisav when Avraham passed away? 15 !!

(Avraham was 100 when Yitchak was born,Yitzchak was 60 when Yaakov and Eisav were born...100+60+15 =175)

So did Eisav behave wickedly at the age of 13 or 15?

Answer

This question is actually asked by the Yerushalmi (quoted by the Daas Zekeinim in @GershonGold's answer) which answers that at thirteen Esav began to sin but it was not yet public until age fifteen. However, the Lubavitcher Rebbe (Likuttey Sichos Chelek 1 pg. 49) questions this, because if so why was it necessary to cut Avraham's life short by five years - Hashem could have arranged that Esav's sinning remained hidden for longer.

He therefore cites the answer of the "Asarah Ma'maros" and Riva"h who explain that after the Akeida, while Yitzchok was waiting for Rivka to turn three so he could marry her, he was in Gan Eden. Gan Eden is higher than the time of this world, and therefore time was "paused" for him there. Therefore when he gave birth to Yaakov and Esav, although he was only considered 60 years old, in fact 62 years had passed since he was born and Avraham was then 162. 13 years later Esav begun to sin and Avraham then passed away at age 175.