I also planned to be "finished by 30". I was the eldest of 9 (DH of 2) and I told him I wanted a large family
However, I have the philosophy now that I'm open to whatever (or whomever) comes
We got married at 21 (DH was 22) and fell preg straight away to have our first 3 in 2 1/2 years and our D 2 yrs later so all 4 were under school age. Not bad for a SAHD (I've always worked full time)!
We had a natural gap then of 3 1/2 years and trained as foster carers but before we took the first kids on, we found out we were having E (I was 31), F (I was 33), G (35) and H after another 3 1/2 yr gap at 38. We miscarried I last year at 40.
I must admit that the older I get, the less energetic I feel but that could be just my general fitness. I was devastated at the loss of I but am just glad I've got so many healthy others.
We also took on an elder foster daughter between G and H who is now a single mum of 3 children under 2 1/2 so I get to be grandmotherly, too. DH began a business from home after G, too, and things got a bit more frazzled about then.
I would never tell other women how many children to plan (none of my business) but I like to reassure everyone that an extra here or there isn't too hard if they fall preg accidentally. If DH can do it, and run his business, anyone can!