I dunno. I think...well, this sounds like it was written by a young person. Older people seem to face little stigma, at least from each other, when they do what they feel, so long as they're not awful to their kids in the process. I don't think anyone expects Grandma not to date, but if she doesn't want to, that's cool too.
I think the early-adulthood stuff is really just about having kids, because it's true, there are limits, even if you're a guy. (I know a guy in his 60s with a second family, kids ages 5-13, and man, it's tough on him. He's old, he's tired, and even though he's retired, those kids are a lot of work. His wife worries about the kids going through adult life without a dad. And I get that. She and I are middle-aged now, and we're responsible for families; we're the grownups, we know how to take care of stuff, and when our parents die, we're sort of ready. I think it's been much harder for friends whose parents died early.) And it is much easier to have kids within a partnered/married context.
I think also this idea of a "life partner"...eh, this is something for young people. If you happen to get one, that's great, but most people wind up single or divorced, with a series of partners. Which makes sense. People change as they go through life, what they find important changes, what they want changes.
So yeah, I agree with the "marry early if you want kids" thing. You can get divorced later -- it sucks, but unless you married someone horrible it's only a year out of your life, and that's with kids/custody involved -- but your parenthood window doesn't last forever.