OP I think you're conflating two issues.
I could try to have a baby now if I wanted to: married, good career, big salary, house, investment property, lots of savings, in good health. I appreciate now (age 32) would be an ideal time to start trying and I am not fully appraised of fertility in the way a biologist or doctor would be but its fair to say i appreciate the evidence and risks.
But I just don't want a child now.
I might change my mind and I'm also aware that if/when I do I might struggle to conceive. If that happens I am sure I will say 'I'm so gutted, if I'd known thus would happen I would have started trying on my honeymoon'.
That doesn't mean I didn't understand fertility, it's just the age old 'I never thought it would happen to me' line.
I suspect the friend you're referring to is just mourning that the dice rolled against her, not that she didn't know that's how the game worked.
Fortunately my friends and family know me better than to try and lecture me about leaving it too late - they know I'm not daft. But I'd still appreciate their sympathy if I failed to conceive later and was sad about it, I wouldn't expect them to take the attitude that 'well even though we'll never know because we have no time machine, you might have conceived a child naturally at 32 and you had no excuse not to so now you're struggling it's your own fault for not bringing a child into the world that you didn't want then'.
If they don't want to try when their biological conditions are better you don't begrudge them that surely? You can't be suggesting we should all just mate for the sake of it in case we try but fail later?