Sayyed Mohammad Al-Musawi,
Sayyed Mohammad al-Musawi is originally from Iraq and heads up the World Ahlul Bayt Islamic League in London. Other than being involved in various humanitarian projects, he frequently responds to religious questions. In the past, he has also spent significant time in India guiding the community.
The most authentic sources indicate that Fatima al-Zahra (SA) was born five years after the Bi'thah (Prophethood declaration ) which is three years after the Esraa'.
and Kashf al-Ghummah by al-Erbali; 1:449,
and al-Manaaqib by Ibn Shahr Ashoob 3:357.
Authentic evidence from Abi Jafar (AS) stated that her birth was five years after Bi'thah. Al-Kafi 1:457 and from Abi Abdullah Al-Sadiq (AS) ; Dala'il al-Imamah 18/79 and from Imam Al-Redha (AS) ; Tareesh Al-A'immah by Ibn Abi al-Thalj.
Some Sunni books narrated different narrations but not authentic as the statements of Ahlul Bayt (AS) mentioned above.
'The age of Fatima Al-Zahra (AS) when she was martyred was eighteen years according to the most authentic sources.