Four of my kids were born during that timeframe, and only one of them is slow to dating. The rest need a bit and bridle to rein them in.
My wife comes from a large matriarchal dominated family, and she likes to run everyone's lives. I love her still, but she needs to butt out of her adult children's lives.
My poor 15YO son has to deal with their legacy, and my wife's efforts to correct her past mistakes by riding his ass. He's at school from 6 AM to 7 wide PM, thanks to sports and band. On top of that, add Boy Scouts to the mix.
IMO, she's scaring the kids away from marriage. I have more patience with them, as I didn't get married until I was 33. If it takes them longer to find the right partner, it will be worth it.