I had my two in my mid - late twenties and it was pretty perfect for me.
By the time I had kids, I'd been to uni, established my career, owned a 3 bed house (with mortgage), had spent a decade clubbing, holidays to Ibiza etc and was done with the clubbing scene, I had met my dh, married, settled and was ready to move on to the next stage of my life.
By having my children in my 20s, I was lucky that my children were able to have a very close relationship with their grandparents who were in their 50s, and their great grandparents who were in their 70s.
Now I'm mid 40s with children in their teens, both will go off to uni over the next few years, both by the time I'm 50. Loving the fact that DH and I are getting our lives back, I'm now studying for my doctorate, and really appreciate it now - far more than I enjoyed studying for my undergrad, or even my masters, which I did in my early - mid 20s. One of my friends had her friends in her early 40s, and I take my hat off to her, I don't know how she coped with the late nights, lack of sleep, permanent tiredness etc. I certainly couldn't do it again now.
But I think the sacrifices for me are financial. Having a child earlier meant I started working part time earlier, so I have a smaller / cheaper house, less glamorous holidays and a smaller pension pot than if I'd had my children later. However, as my children are a bigger priority to me than money, I'm glad I've had my children in my life for longer, and unless I have an early death, I will hopefully also enjoy a close relationship with both my grandchildren and great grandchildren.