Someone may say why fixate so much on one topic which is not even from the necessities of the religion, but the fact is that such a mindset and adoption of the secular humanist morals ultimately leads to heresy and kufr, including rejection of the necessities of the religion and/or expressing hatred and disgust towards them. Also the risk of blasphemy by considering something done by rasulAllah ﷺ to be morally reprehensible and abhorrent.
The issue with the idea of sayyidah aayishah رضي الله عنها being much older is that it is not only contradicting the authentic reports and the agreement of scholars for centuries but it is far more damaging. The reason being is that many of those who hold this idea do so out of discomfort and even hatred with what is authentically transmitted, they imagine that they are defending the honour of rasulAllāh ﷺ by negating her being a child. Whilst this intention in of itself is praiseworthy, the method and result is certainly flawed, and leads to them accusing those who stick to the authentic narrations and agreement of scholars of being blasphemous and attacking the honour of rasulAllah ﷺ. This is the approach of the mini dajjal of Birmingham. What this returns back to is one's moral compass. The reason why the idea of an older age even emerged in the first place was due to the attacks of the kuffar against rasulAllah ﷺ in the 20th century, and the qadiyanis and reformist movements promoted this. But why should we reform and change the sirah based upon the likes and dislikes of the disbelievers? Does this not take away from our belief that rasulAllah ﷺ is the most superior and perfect human, nay, rather the most superior and perfect of creation? If we are to judge his noble life and actions by a modern Western idea of morality, then where is our belief in his perfection and superiority? If we are to alter and change things that are authentic and agreed upon simply due to the dislike of the impure infidels, then where would this end? There are numerous aspects of the noble sirah which contradict what they consider good and morally correct, how much of it do we revisit and alter? The root issue is that of morality. Muslims need to stop aligning their morals and what they consider right or wrong simply due to what is popular today and comes from a secular humanist world view. It returns back to epistemology, once a person accepts Allah as His Lord and rasulAllah ﷺ as His true messenger then they should humbly submit and bow their head to whatsoever they allowed and decided. This is what Islam is, to submit. This is what it means to be a Muslim. May Allah forgive me for any mistakes as I am not a scholar nor anywhere near it, but this is my humble attempt to understand this issue which is among many of the issues that Muslims feel to be problematic morally and so seek reform and alteration of previously agreed upon facts and concepts.