I think OP that if you are considering having a baby, you always have to be prepared for the possibility of having a disabled child/ending up as a carer.
A child can be born with an unexpected disability to a parent of any age. Any child can go on to develop a disease which leaves them disabled. Any child can go on to have an injury or be involved in an accident which leaves them disabled.
When you decide to become a parent, you are accepting that you will love your child no matter what. And that you will hold their hand on their life's path, wherever that path may go.
Of course the risks increase with age, but the numbers are actually still pretty low. Let's pick autism as an example - the risk for OP would increase to 56 children in 10,000. This compares to 34 children in 10,000 for younger parents. There's an increase, but not wildly higher.
Any child can end up needing lifetime care. You just never know. And if you're not prepared to provide that, you shouldn't become a parent, regardless of how young/old you are.
And I say all this as the parent to two autistic DC, who I gave birth to aged 34. Twins - DS has high needs and will be at home with me for life. DD might live independently eventually, but not looking likely right now. So I know what life is like with two disabled teenagers who are still fully dependent, and one still in nappies.
Yes, it can be hard. But I wouldn't ever go back and change my decision to have children. They make everything worthwhile. I love them to bits.
The increase in risk - not just for autism but for everything - isn't crazy high at age 40. If you feel the urge to try for a baby and become a mum at age 40, I can't see any reason not to give it a go.