Intro
Ahmadis have a habit on knowingly lying.  I have found this to be true in every single angle of argumentation that Ahmadis have ever used.  In terms of the age of Ayesha at marriage, there are super authentic hadith in Bukhari that tell us she was 6 at the time of marriage and 9 and consummation.  This was totally normal for that time and era.  However, MGA never spoke on the issue, since it was never an issue before the 1900’s.  Nonetheless, Ahmadi-Mullahs found the need to deny the hadith from Bukhari.

The hadith from Bukhari

Volume 5, Book 58, Number 234 :
Narrated by Aisha

The Prophet engaged me when I was a girl of six (years). We went to Medina and stayed at the home of Bani-al-Harith bin Khazraj. Then I got ill and my hair fell down. Later on my hair grew (again) and my mother, Um Ruman, came to me while I was playing in a swing with some of my girl friends. She called me, and I went to her, not knowing what she wanted to do to me. She caught me by the hand and made me stand at the door of the house. I was breathless then, and when my breathing became Allright, she took some water and rubbed my face and head with it. Then she took me into the house. There in the house I saw some Ansari women who said, “Best wishes and Allah’s Blessing and a good luck.” Then she entrusted me to them and they prepared me (for the marriage). Unexpectedly Allah’s Apostle came to me in the forenoon and my mother handed me over to him, and at that time I was a girl of nine years of age.

Ahmadis lie professionally
Mirza Bashir Ahmad was the first Ahmadi to challenge the age of Aisha.  Feel free to read about it here.

The truth
Professor Jonathon Brown explains it all here.