I think it is very possible.
We could be FIRE if we made a few tweaks.
We are 45 and 43, two kids (7 and 1. Yeah, we waited.)
We have always been good savers, so that's a plus, and are worth quite a lot (both are engineers with decent salaries, though due to location, not top of the line).
What we did "wrong" - bought a house in Coastal Southern California in 2004, that is just now probably getting close to be worth what we paid for it. And it was very expensive. So our choice of location for living and buying a house was very poor for FIRE. If we wanted to actually retire, we would have to move someplace cheaper. As it is now, I could "retire" and we could live on DH's salary. If we moved to a rural area of the country (where either of us grew up), we could both retire.
It especially helps to be frugal/ Mustachian already when you have kids so that you are already in the habit. We've never been ones to enroll our kids in multiple expensive activities, music lessons, etc., because it's not our thing. However we do have a big daycare bill (which would pay for a lot of activities.)