It's naive to ask what is outrageous about telling girls the risks of having kids in their 40s as opposed to their 20s? Let's face it, it's nothing like the Handmaids Tale like made out.
I think if you take that one comment in isolation it would be hard to be outraged about it. But doesn't this already happen? I don't know any women who aren't aware of their biological clock and the increased risks that come with having a baby later in life.
His quote also doesn't make any sense, "We need to also explain to young girls and women the biological reality of this crisis. Many women in Britain are having children much too late in life and they would prefer to have children much earlier on.".
If they want to have children earlier but can't then that is the issue you address. Obviously some barriers, fertility issues, are harder to remove than others but if he is correct to say women want to have kids earlier but aren't then telling them about the "biological reality" will have zero impact.
People are probably looking at this as part of an overall picture of the guy who is also talking about taxing women who don't have kids and making disparaging comments about "childless women".