I don't think it's too late for you to have a baby, there will be risks that you need to be aware of, and given your medical history- definitely keep all your doctors informed and have open communication with them while trying to decide what to do. As long as you are consulting your doctors and gathering advice- make the best decision you can for your family. Best of luck!
Especially since you've already had kids, 41 is doable for getting pregnant. Sometimes ladies who haven't had kids yet have a harder time getting pregnant the first time after 40 for some reason. The only thing is that the 'trying' situation is a bit amplified. I got both my kids in under 40 but when I was trying, my doctor basically was going to have me skip a few things and go straight to fertility treatment if I didn't conceive quickly. I was actually scheduled for IVF when I found out I had gotten pregnant on my own (whew!). I was skipping AI which we'd probably have tried first (cheaper and less invasive) if I was younger. You have fewer eggs after 40 so they try to speed things up for you to make it happen in time before they run out. :>)
I do have to ask about the void part though. What void are you trying to fill? And purple is totally right, you should make sure your doctors are aware. Discontinuing bipolar medication can be tricky as I would hate for you to spiral and have a mental health set back. Hormones involved with trying to get pregnant and pregnancy can be hard to deal with on their own. So, you'll want everyone to be on the same page to make sure you are managing alright.
So, in asking what chances are for pregnancy after 40 are, they do go down. Quantity of eggs go down as well as quality. Miscarriage is more common after 40 as are birth defects. That's just the reality. I didn't test for downs syndrome when I was pregnant because I knew my age would skew the results on its own and didn't want that stress . . . oh, my ob was not happy I didn't do that testing. But that was my choice. I do have a son with a developmental delay but have no idea if it was related to my advanced maternal age or not. I think not but who really knows? right? And I love my kiddo to death even with the extra challenges. I did also have pregnancy hypertension which has an increase of happening with advanced maternal age too. Things like that are more common the older you are. So, you'll want to know about these things and be prepared.
But a lot of women are having babies in their 40's and all is fine. So I wish you the best and hope it all works out well for you! Keep us in the loop!.