I agree that 30 is way too old for the game start. For the time period you'd already have 5 kids by that age. Why are you even still living at home with your parents at 30?
I hope that the 30 yrs old was just an arbitrary number that they set without really thinking about it and nobody changed it yet. It really should be 18 or 20
Not everyone can get marriage, not everyone can get family or children, some might live with parents, because parent unable take care or children can't take care of themself, mostly because disability, or save lot of money or make life more bearable because economy wasn't good for common low income, ect. Some don't had choice, some had choice, many had reasons, so guess.
Beside very, very rare people had 5 children in 30, Most I know and common is they don't had children (well, for men more often are childless than had a child, but women on other hand had children more than childless), often had 1 or 2, fewer but yet many may had 3 but not 5 at least, very rare.
I don't know why you think everyone should had number of children, I'm petty sure more common people don't had children or very few than had manys. More and more common children do live with or parents live with children, due economy is so bad for low income people, thought often roomate/friend live together to save money, not much difference live with family (whatever parents or greatparents or uncle or even family friend.
I guess back in long, long ago it's easier to children go out and get own land even it's free but had to work hard for it, but today, too many people, there is no free taking land, let alone land tax (there was no land tax, just income tax in ancestral time, even no tax at all, if you are strong or very well hide like live in forest where lord or king had limited to reach, but today IRS, Goverment's force can get anyone on anywhere ensure no one outrun their scam of tax.
Even you work hard, but unreasonable cost of money and even unreasonable law/policy blocked way of get tax free land to live on it, unless you are rich or good income to cover cost. It's not like old day where children can or able to move out of parent and get land for free but had to work on it or build it, but you can't do that today where goverment and too many owner had almost all land on this world where there is no free land to live on, so most end up live with someone by mostly not choice because too many people live on earth, too much goverment power where make you pay for living on land by bully.
Come to think of it, I think children in ancestral had more freedom and more to grow, yet it's more danger than today, while today it's more safe than back in time but limited freedom, limited grow.
Oh, I'm not sure but common parent in back in time hopeful children live with them when they are in age, children in return taken care of aged parent, I think it's common at least one children live with parent, along child create family along with it to taken care, but today in american, children dump or parent end up live in nurse home, ect due because it's could time, cost, career, new family or had no strong bond, I guess even long ago parent and children might had boud even they hate each other but I don't think children and parent had strong bond today in american but rather weak or none of it, at least.
There is no nurse home back in time, so children are one who take care of parent so often parent live with children or children live with parent along with new family children married to, but I guess rich can afford to get away or had a slave or servant to take care of them, while poor depend on children.