Not much to add other than that as the dad of 2 girls aged 15 and 11 it is really sad how much excessive thinness is promoted in US culture. My 15 year old is maybe 5’5" or 6". Really healthy. A dancer who can do 50 pushups. And she was all worried when she discovered that she weighed 130#. I defy anyone in their right mind to look at her and see anything other than an incredibly healthy young woman.
My 11 year old, on the other hand, is a cute little pixie. But she would often go without meals if not encouraged to eat. As of yet she is not TOO thin in my eyes, but we are keeping an eye out to make sure she doesn’t tip in that direction.
Girls come home from school in grades 1-3, asking if they are fat. I know childhood obesity is a growing concern in America, but it really is sad to hear healthy - even skinny - little girls sound concerned over their weight.
The previous responses are consistent with my opinion that it is entirely a personal choice. The reality is that none of us look the same at 30-40 as we did at 20. And a new dad may have a hard time conceiving of the toll pregnancy takes on a woman’s body. It would not be unique for your bubby to think, “Heck, I’m still in shape. Why has she let herself go like this?” Fortunately, with most sane men, this passes. Especially when the women’s 30-ish sex lust kicks in with a vengeance.
I personally was always a tall, rail skinny kid. Now I dislike it when I have to go up a waist size. Not only because I prefer the way I look and feel when I am thin, but I don’t want to go out and replace all of my clothes. And I hate the thought of giving up more and more ground every year. Of course, the joke is to keep buying more and more “relaxed” fit pants, and you can magically retain the same measurements! 
For me, if I put on a few pounds it is a sign that I have been especially sedentary or hitting the feed trough too heavy, and I am able to take it off quickly. But at 42 I have accepted a baseline of 10 pounds higher than when I was 20-35.
Oh yeah - men ARE pigs and will continue to check out young gals until the close the casket on them. But looking is just that. And few men “of a certain age” are fools enough to think the young fit women even notice them in return. And they no more expect their wives to model for a pin-up spread than they themselves will go into a pose-off with the 0% fat high school/college studs at the community pool.
Get comfortable inside your own skin, no matter how much of it you have. In most cases I believe “fat” is an attitude more than numbers. I have none several really obese women, but the term “fat” would not come to mind describing them if they were intelligent, lively, funny, etc. But, if they dress sloppy, carry themselves poorly, and display no personality, their weight seems to come to the forefront.
