Were Umar ibn Al-Khattāb and Husayn ibn Ali alive at the same time?
Yes. Umar ibn Al-Khattāb and Husayn ibn Ali were alive at the same time for 18 years, from AD 626 to AD 644.
Husayn ibn Ali was 18 when Umar ibn Al-Khattāb died.
Husayn ibn Ali
Grandson of Muhammad and the 3rd Shia Imam
Born 9 January AD 626 · died 10 October AD 680, aged 54