I'd recommend going to a shopping mall, just sitting, and looking at women going by.
One thing becomes immensely apparent - the assumption that age must mean surgery actually goes down. I cannot tell you how many women who look 50+ also have some masculine facial features. As menopause kicks in, there are minor changes there too.
Now, having said that, many of those women are not what would be considered beautiful or particularly pretty anymore. But that's age and loss of hormones at work. And this is where FFS can help scads for an older trans woman. In some cases, it can take an older trans woman from being passable to being a beautiful older woman. In more cases, it can take an older woman who cannot pass into one who can.
I will also state two other things - most trans women do not need FFS, but they would benefit from FFS. I plan to do so myself despite passing easily at my age (still part time) and despite friends insisting I look "fine". I tell them it's as much for my own psychological peace of mind as anything else and they say they then understand that.
The second point is that the vast majority of people out there are not looking at every passing human being asking, "Is she trans? Is she? Is she?" Get that out of your mind! If your appearance, mannerisms, dress, and voice all come close to conforming for female norms wherever you live, you are likely to pass just fine. People trigger when something glaring leaps out at them, and I mean glaring, like a good looking transwoman who opens her mouth and speaks in a rumbling baritone.
To Carrie Liz, yes I've seen numbers that 1 in 500 or so are likely to be trans. But I've also seen reasonable estimates that only about 15-20% of those actually transition, for whatever reason. So the actual number on the street is probably closer to 1 in 2500 or 1 in 3000. So not quite as likely as you said but yes, if you work in a metropolitan area and go for a walk at lunch time, odds are pretty good that you walked right past a transwoman somewhere.