I'd like to posit that "back in the day", people's lives had reached a max in their 20's after they finished school, got a job (unionized and/or indefinite contract), got married, bought a house, started having kids, etc.
Nowadays, school will take longer because you need it to make a decent living - there's too many low paid jobs. Second, to get married and buy a house and such, you need a decent income. To get that, you either need a high education and live in an area where you can use that, or work multiple jobs and have no time for a social life, or be lucky and get a middle class paying jobs in an affordable area.
So it's not just a personal choice from ambition, like you're suggesting, but it's also that the previous generation had it easier. They had the option to work where they live, to buy a house off of that money, and do it all before their 30's.