*The very best age to have children is when you're ready. It can turn out fine if it happens and you're not ready, but best is when you want.
*
Pretty much this.
Mine was 34, 37, and (will be) just turned 40. Wouldn't have wanted to do it earlier, and not just for career reasons - though you're going to take a career hit whenever you have kids, so there's a question of when that hit will be least hard - for me that's definitely now, as I'm senior enough to have a financial cushion, and flexibility in how I work (as I'm more valuable to my company now than when I was 28).
But there were also relationship reasons: I was with my DH from 25, but we wanted to enjoy loads of time with each other before adding children into the mix and I don't regret that for a second.
And there were life experience reasons - for me 25-34 were (very fortunately) years of having just enough disposal income to do fun and interesting things (travel, a masters, renovate a flat, learn new skills) before being constrained by children (because young children do constrain you, even though I'm general happy to be constrained cause they're great).
Basically my children are amazing and my life is richer for having them, but it is also richer for having all the things I had before them. Some people will be ready at 28, some at 38. Don't let other people rush you (and don't get overly hung up on fertility: obviously it declines with age, but 35 is not a cliff edge - look up the more recent stats, it's something like a 27 year has a 92ish% chance of getting pregnant within a year of trying, and a 38year old about an 86% chance in same period. It's not rare to have children in your late 30s!)