Hi D.! Hope you're doing well :)
I think it depends on lots of things- here is a list that I would think about:
-Are you willing to accept that you might have a down syndrome child? There are tests that you can take that tell the chances your unborn child has of having certain defects, but some can be invasive and stressful. You would have to think if you would be willing to raise a child like this or terminate the pregnancy.
-Would your age matter to you in that it might be harder for you to participate in life events of your child? I would worry that if I was in my 60s and my child was in his 20s that I might not be as able to help them move into their first apartment, etc. etc. just due to physical limitations that come along with age. Of course, there is the upside to this too, because he/she would have brothers and sisters that would hopefully fill in these gaps.
-How would your children of childbearing age feel about this? Would it impact your relationship with them? On the parenting boards I often see mom and daughter both preg at same time and daughter is VERY distraught because mom is getting more attention (or not able to give the daughter her attention) because she is also pregnant.)
Hmmm.. that's all I can think of right now. I'm pregnant myself at 29 at the moment and I'm feeling VERY much older than when I had my daughter at 22. Not that it might have been any different if I had had another at 24, etc but I do feel like I have more aches and pains this go round, as well as allergies I've aquired over the years, injuries I've sustained, general wear and tear from age, etc. It was my personal decision NOT to have children over the age of 30 for myself, but that is a very personal decision to make and I don't mean that as a judgement on you by any means. I want to be young(ish) while my children are young and be able to travel, etc with them when they are older as well.
Having said this, my husband's parents are in their early 70s and he is 31, and they are both in excellent health with lots of energy for the grandchildren, travel all the time, go on bike trips cross-country, etc etc.
Hope this helps some!
If you have anything you're thinking through and want to bounce it around with someone else, feel free to contact me off-list :)
M.