Discuss it with him and say no.
He doesn't get to decide a single thing about your body/health. At your age it would be far more tiring and difficult to be pregnant than it was 14 years ago. That's just a fact, no matter how much some women wish it was not true.
Every pregnancy carries risks for the mother of heart attack, stroke and death and other issues with your future health. Yep, every pregnancy. Yep, that's a fact. Small risks, mostly. But definitely true.
Adoption means no risk to your own body, but still changes every single thing about your life forever.
Some daft bint earlier was like "Well, he might leave you if you refuse to be his incubator" so just to address that - if that is the case you are FAR better off not having a child with him. If he's such a selfish creep he that he'll leave you for not wanting to completely disrupt your life and your body and change everything forever on his whim, he will definitely leave you anyway and you will be left with a baby in your forties and all alone.
And, all of that aside, you don't want to. So that's that.