Engaged at 22, married at 24, first kid at 27, third kid at 30. Husband ages here, subtract 1 for wife.
We had a few short term things that made our timing silly (wife finished last grad school class on maternity leave, professional certification that should have taken 6-12 months took 3 years, oh well). That said, the friends of ours that waited a few more years might have established themselves, but they are disasters with the kids. A career is no less derailed at 35 than 25, it's just that at 25, you're expected to be a disaster, and at 35, people expect you to have your shit together.
I think when you decide you're ready, put together a punch list of "shit I need to do while I control my time" but make sure it is < 1 year, doable, and you're on track. The more ducks in a row in the financial/professional side, the more you'll be able to handle the deluge of crap that is a new born.
I'll also say, as the kids get older, being a "younger" parent is HUGE. Being able to sign up as a Scout volunteer and be able to keep up with the kids is great. The older FIRE parents I know simply don't have the energy, even if they have all the time in the world.
Something to be said for keeping busy, when I'm busy as hell I get everything done and don't know how. When it's slow I meander through things, doing stuff like posting on this forum instead of running full speed.
So that's my suggestion, as young as you think you can handle + 1 year. :)
In terms of wanting everything together... from the moment you get pregnant it's nearly 1 year until you have a kid, definitely a year before you're thinking day care, and 6 years before school starts. You don't need a house in a great school district to have sex with your partner. :)