Confidence and the way you carry yourself. In our teens and early twenties we tend to dress and act for others. As we get older that becomes less common, or we become better at selling our appearance (attire, demeanor, etc.) as ourselves and not a façade. Whether that's a hoodie and jeans and converse sneakers, or a suit and tie, or something in between doesn't matter (mostly).

Also, in your twenties you're still putting on muscle mass and filling out some. If you maintain decent physical conditioning you won't have that scrawnier look that a lot of teens have. You probably have broader shoulders and a fuller face than you did in your younger years, it looks healthier and more attractive, even if it's paired with gray hair and wrinkles.

it actually doesn't, in fact it grows continuously, but you'll just be shamed by older women and married men for dating younger women.

Select every argument about why it is none of their business to outlaw/shame homosexuality, Ctrl-C, Ctrl-P.

Why would it? If anything the number of single adults keeps growing each year.