You're SOL on your height, but your muscle mass is quite malleable with pretty low effort. I work out for two hours a week, one hour on Saturday (upper body), one hour on Sunday (lower body and core). I don't look like an nfl linebacker, but it gets me to the athletic end of the dork spectrum at least. I'm betting you can find two hours a week to spare. If it doesn't take, you might have low testosterone, which is easily fixed medically (by taking testosterone, ie anabolic steroids... kind of extreme, and for the record, I don't take them myself, but if you actually have low t it seems somewhat reasonable to me.). Even if you don't want to work out, I don't think being short and skinny is a huge barrier to getting girls. Many of my friends fit this description and haven't had trouble. If that describes you, you may have other problems. If you've left unsaid that you're overweight, that's a lot harder to fix than muscle mass. Probably worth one good attempt to slim down, it works for some people, but doesn't for a lot of others. You may have to live with it.
Which brings me to... social skills. They really are skills. It comes naturally to a lot of people, but if it's unnatural for you, you CAN get better if you try. It takes a lot of effort, but if it's important to you, put some real effort (and time) into it.
Females are not as irrational in their preference for tall muscular men as you seem to think. Tall men make more money on average. So do good looking men. Why? There's two sides to any business: making shit and selling shit. I'm guessing you're good at the making part. Selling is just as important. People like to be around attractive people. Sucks for the non-beautiful, but just a fact of life. But you know what? They also like to be around funny, confident, and friendly people. And you can do something about that.
More height means you have more cells that could potentially become cancerous.
Wow, no shit:
http://www.wcrf.org/int/blog/articles/2015/09/why-taller-peo...
Not exactly the mechanism you proposed, but still...
By the way, a large majority of humans in the United States marry and even among the ones who don't marry a vast majority of them have dated. A large majority of people in the United States are not tall and muscular, we come in all shapes and sizes.
You may find this shocking but Women aren't uniform brainless sheep. Women come in all forms with all sorts of different things they find attractive. For example, I don't find muscles especially attractive and tallness does absolutely nothing for me. My husband is overweight and I don't mind a bit, doesn't distract from his attractiveness to me. Some women are even attracted to other women.
(Hint: it actually might be you since 99% of society can somehow manage to get a date)
Looking at japan, that number seems overestimated. That might be your personal experience, but because of survivorship bias - you'd be less likely to meet antisocial shut ins etc.
