With regard to the marriage of Aisha (RA) to Rasul it is possible that the hadith could have got the ages wrong...people in the past did not know their exact birth dates or ages.
Some scholars may consider a hadith to be authentic and another may not but this is always on the basis that there is some weakness in the chain according to one of them and not according to the other. Hadith are not declared to be weak or fabricated just because it is incomprehensible to the mind of Imran Hosein that our Nabi would do something that he (Imran) personally does not understand such as the marriage of Aisha (RA)