It's very doable, especially if you have a partner to split it with. Where the $45k gets someone under 30, is just that it can take several years to put together that sum. Most people don't start to hit their earning stride until the very late 20s or early 30s.

So you're in the median bracket and you get your first serious, solid paying job by ~24/25. It's reasonable that if you're diligent about savings every month, you could have $45k+ by yourself at 32-36 years of age, and I'm assuming some financial setbacks along the way. With a partner, it really shouldn't be a problem by those ages. To do it before 30, you'd need a good economic pairing of two people that already are near or above $85k by 30. All assuming you're not living in an expensive market of course. With the necessary caveat: having children before 28 or 30 considerably changes the equation (unless you have a larger income in the household to offset that additional cost), as can serious health problems and associated bills (depending on your job/career situation).

Don't forget student loans. We have a whole generation of people that are saddled with large student loans. They can easily spend all the money that would have gone towards saving for a house downpayment on paying their student loan payment instead.

Marriage-related crap is charged to credit cards and/or is subsidized through financial gifts by friends and family after the wedding.

Down payments are neither, unless your parents/inlaws are feeling generous.

The average savings account balance in this country is far less than 45k. You are completely out of touch if you think the average family can simply pull that out of their asses.

Marriage rates are also declining except among the middle to upper-middle classes.