How old is too old

To have a baby? I belong to a message board at a fertility charting site, and there are a bunch of women who are in their late 40s, and early 50s that are trying to conceive. One woman has 10 kids, and at age 52 is trying to have another. From the sound of her posts, her husband is not thrilled with the idea, he's reluctantly supportive at best. How old is too old? I think at 52 it's a bit unreasonable, you are at best beginning menopause, and pregnancy can be dangerous. My mom had my brother at just 36, and it was much, much harder on her than her pregnancy at 18 with me. What do you think? Would you be actively trying to have a baby at that age?