At the time of Nikkah, Prophet's age was 57 and Hazrat Zainab was at 36 years of age on 5th Hijra. She passed away at the age of 53 on 20th Hijri and buried in Jannatul-Baqee, Medinatul-Munawara.

Source: http://en.wikipedia.org/wiki/Hafsa_bint_Umar

She was married to Khunais ibn Hudhaifa but became a widow in August 624.

As soon as Hafsa had completed her waiting period, her father Umar offered her hand to Uthman Ibn 'Affan, and thereafter to Abu Bakr; but they both refused her. When Umar went to Muhammad to complain about this, Muhammad replied, "Allah will marry Uthman to better than your daughter and will marry your daughter to better than Uthman."[3]

Muhammad married Hafsa in Shaaban AH 3 (late January or early February 625). This marriage "gave the Prophet the chance of allying himself with this faithful follower," i.e., Umar, who now became his father-in-law.

Hafsa is viewed very negatively among Shia. Several prominent Shia accounts report that she, along with Aisha, brought about Muhammad’s death by giving him poison.