Obstetrically, 24 is said to be a good age. Generally speaking, I'd say mid-20's to early 30's. People aren't really finished maturing until then (the skeleton and brain are just finishing up maturing), but waiting until 35 can mean running into increased risk of fertility problems or other problems.
Speaking only from personal preference, I think late twenties to very early thirties is ideal. Besides believing the more mature someone is before starting a family, the better; I think it's nice for women (and men) to be able to spend most of their twenties as young adults who don't yet have the responsibilities and worries of being a parent. It gives time for a little extra education and career building (or just for living as a young, childless, adult).
On the other end of things, I have found that I think having my children in my late twenties, with the youngest (third) at born when I was 32; I've gotten to feel younger that much longer. I'm just going through the emptying of the nest now, and I still have lots of time to "just be me" before becoming a grandmother (if I'm going to be one).
To address the myth that mothers who have their children just that much later don't have energy: I have far more energy now than I did either before I had kids. I really think some people who feel tired past 40 are tired because of their lifestyle (or something else). OR, maybe when someone is 44 and has a 24-year-old they just feel older and more tired than someone who is 50 and still has a son or daughter still in college - I don't know....