I am 49, with 2 young adult children, I don't own my own home, I rent a social housing property, (with DH,) I work part-time, and pick up £200 a week, I don't own a property, OR a car (I use DH's if I need to,) and only own a bicycle.
I love playing video games, collecting beanie babies, going to pop concerts, crafting, long walks, swimming, reading shit magazines like take-a-break, watching shit tv like Love Island, reading crime novels, writing short stories, having mp3 parties on my own, and stargazing at midnight. I have no fancy, expensive pastimes....
Me and DH have £1500 in savings, no 5 figure sum in an ISA, no home of our own, (and definitely no second home.) I am not a professional, I do not have a university degree, I earn 75p an hour above minimum pay, I have several 'bonkers' family members, I like a couple of bottles a wine a week, I don't plan big expensive holidays waaaay in advance....... Oh, I have a small pension (and so does DH,)
So I guess I am not a 'proper grown up' at nearly FIFTY years old?!' 🙄
What a thoroughly ridiculous thread.
And what a laughable attitude, to assume because someone is (supposedly) wealthy and owns more than one property, that this makes them a 'proper grown up!' You sounds about 12 years old @RedZebra 
As has been said, a very small percentage of people fit the criteria in the OP, and although many people on here claim to have paid off their mortgage by 30, in real life, the vast majority of people have not, and very few people know anyone who has paid it off at that age.
Like someone said, mumsnet is a parallel universe, where many posters make outlandish claims of lives that very few people in real life actually have.
Just remember that people can make up any old shit on the internet. Doesn't make it true. And much of what people claim is exaggerated or pure fantasy.
So don't lose any sleep over this fictional 'perfect upstanding citizen' RedZebra 