Bummer, Bifumus. That's a tough one. It is tough to feel the disappointment. I think it's kind of odd for him to ask you about it at 38, too, as someone else said above.
I would list that, maybe, as one of your top ten reasons. You can cite statistics on what can happen to the mother and baby if they have a baby later in life. But I would include all the other reasons, too. It sounds like your life is very full, and you might even say we won't know where we would fit kids in. You might also want to say that we are all born with special gifts and talents, and that parenting doesn't feel like your calling - that you'd like to contribute in another way that is more meaningful to you.
Lastly, don't take the guilt on. It doesn't sound like he's intentionally trying to make you feel guilty, but just because it's there doesn't mean you have to own it. Just acknowledge it and let it go. It's not on you to do something you don't want to do for the next 20 years to make someone else happy! I'm sure if you find a way to communicate that, he will somehow understand.
