Oh OP, I wish I could wave a wand and put the clock back.
You know perfectly well (and PPs have described in detail) why this is a very, very risky idea. If you're anything like me, though, no amount of rational advice or common sense will silence the bee in your bonnet, so good luck whatever you decide.
I'm in my 60s now and have to say that despite looking after myself, I'm slowing down and gradually losing energy. Bringing up a child is incredibly hard work, mentally and physically. There are plenty of threads on this. Many young, healthy mothers wonder out loud why they bothered embarking on motherhood.
What do you think about, when you imagine your child? I'm asking because what seems to happen in real life is that people hardly ever get the child they expected (assuming you are successful). It's hard enough adapating to that if you're young and in a solid relationship and have external support, but how would you feel if the child turned out the opposite to what you'd hoped for? How would you cope with the sullen teenage years, if you'd devoted yourself to giving them everything you ever wanted in your own childhood. only to see it completely unappreciated? If all your lovingly shared wisdom was met with contempt? This happens in many parent/child relationships, nothing to do with an age gap, but the age gap might make it harder to bear because of your diminishing energy, especially if you're doing it alone. 💗
I wasn't the child my parents expected, and I am glad that we eventually reached a loving mutual understanding, but it took a lifetime. I mean, a lifetime. If you had a relationship like ours, you might not be around to see it all come to fruition.
I've noticed this really bizarre thing, which is that at age 65 I started wanting a child for the first time in my life. It's probably because I feel safe and settled and comfortable at last, but it did surprise me because I always assumed hormones were what drove this urge. Obviously there is nothing I can do about it.
This is what cats were invented for!!!!!!!!!!!