I don't really understand the question in the OP. Surely the way in which we remember her, in respect of her age, will be determined by how old each of us is? Younger people will be likely to remember her as a significantly old lady. Older people will have memories of her as a middle-aged woman as well as an old lady. And since our earlier memories are more likely to be formative , thoughts of her as middle-aged might be more iconic and salient for us than some of the more recent memories.
I don't really think that any of those individual variations in how she is remembered determine a collective truth about how Brits regard her.
Because she was significantly older than most Brits around today, I think that most of us see her as a 'link to the past'. Even in my youth, when the monarchy still seemed moderately relevant and integral to society, it was already perceived as increasingly archaic. Her status in the public imagination was as a figure that linked history to the present.
The difference now is that both society and the royal family itself have moved on so much that there is now no real significance to that link. It has dwindled into content fodder for period TV dramas and social media.
I think her death was pivotal. By living so very long she preserved some shell of the time when the monarchy had a little bit of genuine traditional and sentimental meaning.
As soon as she was gone, it became much more evident what the monarchy is now: a D-list celebrity gossip machine, buoyed up with inherited wealth and opportunities for money making that are either shady (Prince Andrew) or tacky (Harry and Meghan)