The reality here is that for everyone you see painting a rosy picture, there will be another in a miserable relationship or fighting a custody battle with a dick of an ex boyfriend/girlfriend/spouse. Comparing yourself to others, particularly from carefully-filtered social media posts, is not a good idea.
My own moment of jealousy came from someone I was at school with buying a fairly expensive car whilst I'd just graduated and barely had a pot to piss in. He had a job that was just over minimum wage and I was utterly fuming about this wondering why I bothered. Turns out a relative died and left him money, and he ended up having to sell the car a year later as he couldn't afford to run it. But on the face of it, I'd only seen half the story.
Take things at your own pace. Marriage and kids in particular are not for everyone, and shouldn't be rushed into just because society thinks that this is "normal". Same with buying a house, tbh.
For the record, I turned 28 this year. I've been married 3 years and own my flat, but don't have kids. But then, I am a right boring b*****d. My own sort of existential crisis came last year when I was concerned I'd be stuck in a decently paid, but dead end job. I got out, have a job that pays well and has excellent career prospects. But it want as easy as that - it involves a 1hr30-1hr40 each way commute every day, and an obscene amount of money spent on travel (the extra pay only just covers it). Sometimes it also involves long hours, which are not ideal.
It was a big change in lifestyle and one my wife wasn't overly pleased with given it means less time at home. But, it has been worth it and I'm enjoying my working week a lot more despite the travel. This was a move I had to make before we had a family, or I'd have been stuck where I was, unable financially or practically to make the move, as the adjustment would be too difficult.
My situation is obviously a lot different to others on here given the posts so far, but I believe the core message is the same if you're in your mid 20s. Make the changes you want to now before it's too late.