I had my third child when I was 38. I had #1 when I was 33 and #2 when I was 36. It was harder on my body at 36 than when I was 33. But it felt the same to me having a baby at 38 as it did at 36.
We started trying for #3 when #2 was still nursing. I ended up miscarrying. I got pregnant again when #2 was 18 months old. The funny thing is that I think it would have been easier to raise #2 and #3 if they were born closer together. (#2 is so much easier in temperament than #1 or #3.)
My kids are now 6, 3-1/2, and 15 months. I'm a SAHM and I'm managing just fine, although life is busy. I wouldn't mind having a fourth, but I'm very satisfied and feel complete with three. My sister had her fourth at the age of 41, so that gives me hope that I still have time to decide whether or not to have one more.
I am turning 40 this year. Some of my friends from high school (same age as me) are grandparents already! It's weird to me to think that my children are the same age as their grandchildren! Anyway, I don't think your biological clock is ticking too loudly yet. You have still have plenty of time. Good luck to you!