I don't wish I'd waited to have kids, but I do wish I had studied before having them. I left school at 16 and worked in low paid jobs until getting married and having kids. I still can only get low paid work and find it really hard to study now with little ones running around.
I had mine at 22, 24, 28 and 30. So if had finished school and gone straight to uni I still could have had babies at the ages I did. I'm glad that when I'm old enough to retire my kids will be old enough to either have left home or take care of themselves while DH and I travel. (we already have a few plans of where we want to go.)