You've got nothing to lose by giving it a go. A man would apply if he didn't meet all the criteria...
If you don't get this one, there's nothing to stop you looking for a similar job in London. There are loads of accounting jobs on the market at the moment. People keep resigning at the moment - many stayed put during lockdown but have now reached peak frustration and the Great Resignation is in full force. The market is very buoyant.
I have to say, I think a degree for an AAT job is ridiculous (a large number of people with AAT didn't go to university) and it's also a bit ageist, given whilst it's common for most young people these days to have a degree, if you qualified back in the 80s, I'd expect a degree to be less common.
As someone who works in the field and who hires in the field, I'd look past the degree requirement (and also shout at whoever put the job spec together). I wouldn't be massively happy about you not having a current AAT membership, particularly as you changed roles rather than retiring, so you actively decided to stop being an accounting technician, but this would be massively mitigated by your current job, which proves you do still know some stuff.
Age and weight are not issues. What is a concern is whether someone who has retired still knows how to do accounting - I've seen many examples of people who have just forgotten.
What did you do to get your current job? Presumably you did some kind of CPD to get back in the game? I think I'd want to see your cover letter/CV/interview stress that you've already been reskilling by attending various (not necessarily paid for) webinars. I'd want to see evidence of that kind of proactive attitude. If I believed it, I'd get the company to pay to reinstate your AAT membership.
As you don't have a current membership, you're effectively QBE. It's unlikely I'd accept QBE from a younger person given in today's marketplace it suggests they weren't good enough, but I would accept it from an older person given the qualification landscape was different many years ago, and I've worked with some brilliant unqualified older people.
Although I don't care how old someone is (it makes no bones to me whether I'm managing a school leaver or someone who could be my parent), I do look at age when it comes to formal qualifications and my expectations do differ there. My expectations are the same when it comes to practical experience and ability to do the job, but I know it was more normal to not get qualified many years ago, and an adjustment does have to be made for that.
If you're not happy in your current role, look for another. It might be this job, it might be another. But don't let your age, weight or AAT membership status hold you back.