Mathematically, for a female living where you are, it's juuust about 41
If you're basing that on a life expectancy of 82, then how can one single year countg as middle aged? We already have a term to describe somebody who is 41 years old, but 'middle aged' is clearly an age band, is it not?
I know people are taking it as being about your attitude to life, but to me, it's just a simple statement of numerical fact. I'm happy to consider myself MA at 43 and have since about 34/35. To me, it's not a description of how little time I have left, but carries a positive sense of progression through life.
Everybody wants to be young, but I don't see young necessarily as a good thing unless you are young.
Would a woman want to be mistaken for a man? Would a man want to be mistaken for a woman? Most probably not. Does that mean that one of them is better or worse? No - it's just your own personal life circumstances and who you are.
Toddlers are often very amusing and cute, and so loveable, but they're also very needy, frustrating, hard work and thankless. Nobody likes an adult who acts like a toddler.
Teenagers are often volatile, moany, frustrated, irrational and trying to find their way in the world whilst being driven by a sea of hormones. I have teenagers in my family whom I love dearly, but I'm glad that stage is now behind me.
People in their 20s and early 30s are often still living in a time of great uncertainty. They frequently haven't found their life partner, career/life path, settled into their own homes, had any/all of their children, are often still very dependent on their parents. I'm glad I've settled down, have a lot more certainty to my life and a realistic outlook of who I am. I feel I've matured (which I consider a good thing) and learned a lot in the years since then. It's a very exciting time, but also very fraught, and it isn't where I am any more.
From your mid-30s until maybe about 60, it's a time when you've come to know who you are, what your life is like, you've gained experience and confidence, are reasonably established in whatever your life turns out to be and, all being well, no longer live in a state of capricious wildness and uncertainty. Nobody knows how long they will live, but this is your time, for as long as your health, mind and body hold out - which might be another 70 years. In a sense, you've now reached the pinnacle of your life - you've 'arrived' and you're a proper, fully-fledged adult, with your own independence, agency and maturity to enjoy it.
Once you reach 60, you've passed into early old age, but that has no bearing on your attitude whatsoever. Your age is a statement of fact, but it doesn't have to completely define how you live. You could have another forty years left still - mortgage-free, children all fully independent, hopefully financially stable and in no doubt whatsoever of who you are, how you relate to the world, how the world relates to you and how you choose to be you, having had the chance to be brimming with wisdom and experience (although some will have firmly declined this opportunity!). Yes, your healthis probably not as great as it was, but remember that, when your body was at its peak potential, you couldn't walk or talk and had no knowledge or control of when you were going to poo and wee yourself, so it wasn't that amazing. Your life may still be boring and mundane, but you have had the necessary time to have clearly carved out exactly who you are and what your life represents. To put it more simply, which would most people prefer: a Lamborghini with 60,000 miles on the clock or a Micra with delivery miles?
Also, not wanting to end on a negative note, but in world terms, the average age of all the people on the planet is 25 - so on that reckoning, if we split it into 3 bands, you enter middle age at about 17 and old age at 34.... sobering.