Why is it so hard to be taken seriously when you are female and don’t want kids? You may change your mind in the future, really? Some people, females included, just don’t want a kid. It’s that simple.
Why is it so hard to accept advice from people who went through the same experiences? Sure in this case a man said it, but there's a good amount of women that didn't want any kids and later on changed their minds, and sure enough there are women who didn't change their mind and regret nothing.
When you're in your 20s, regardless of you're gender you're still young, you learn and grow every day, you preferences change, so do you opinions and choices, and you can feel like you've matured with each passing year.
I hate people undermining our decisions, and saying you'd definitely chnage your mind, but there's nothing that's absolute, be open minded, open to the idea that the people saying it mean well and just don't want you to regret (with regret I don't mean to go have a baby).