I mean... well done to your kids, but there are lots of variables here.
Not all people are in stable/committed relationships at 23. You can't compare buying solo vs as a couple
Some people live in high cost areas - buying a 2 bed semi in say most places in the North East is wildly different to buying a 2 bed semi in Cambridge for example.
Did they have any help with a deposit? Not all people do.
At 23, a lot of people have lower end paying jobs, so combined with the above factors, it's hardly surprising that some wouldn't get on the ladder.
I'm "fortunate" in that I'm in the North East. My 4 bed detached is worth around £250k or so. With a 10% deposit of £25k, I'd be looking at around £1,300 ish monthly payments. To buy my house somewhere like Cambridge, I'd be looking at the better part of £650k, so that's a £65k deposit, which would be around £3,300 per month. Now, obviously a 4 bed house isn't your typical FTB property, but people in some areas are looking at potentially more for their starter homes than I would pay if I was buying my house now, and unless you've got a great deposite from an inheritance for example, getting that on your own is never going to happen.