@Oldermumhum
I had some very similar circumstances to you, down to having my eldest at 31. I didn't particularly feel like an older mum, but I had been having "When are you going to have kids?" queries for a while because OH and I had been together since we were teenagers. I wanted 3 as well.
We'd been waiting for me to finish a Master's degree and my OH hadn't been very well, but his health was doing better and we finally went for it. I had a second at 33 (which was a bit of a short gap: 2 under 2 was exhausting! But I was worried it would take a long time to conceive. It didn't.)
Unfortunately OH's health, which turns out to be a chronic condition, took a downturn when 2 was still a baby and has never entirely recovered. He was pretty poorly for about five years, and meanwhile I had mild PND and a few health problems as well. So the right time for number 3 just never came.
I felt quite regretful (even resentful!) for several years. It feels a bit like pointless wallowing now, but at the time I didn't seem to be able to help it. But a little bit short of my self-imposed deadline for having number 3, I suddenly realised we were done and I was OK with it. We have a lovely couple of kids who are good pals and good company, things were going better on the health front, and our life was starting to be less like hard work.
Would I like circumstances to have aligned? Yes, and I know number 2 would have liked a sister (not that you can guarantee that!) but I am happy with where we are now and wouldn't launch back into nappies and broken sleep and tantrums.
Whether it happens for you or not, I hope there will come a time when you see your family as yours, however that looks in the end, and don't feel regrets. Anything could happen! You might have twins on this go-round. You may feel much happier and raring to go for another at 40. You don't know yet.