I don't think my life has ever, really felt that way.
Only for one year, where I dropped out of high school and played Call of Duty 4 for a whole year.
But other than that, I feel like I've always had responsibilities? Whether they be my education or work. When I was younger I certainly didn't feel like I made many meaningful choices about anything, like attending school wasn't a choice and so forth, but I didn't feel like I had infinite free time either.
I agree, the "when you're a kid, you have INFINITE FREE TIME" thing has always struck me as a bit odd as I didnt feel that way then and looking back as an adult I still dont. I guess it feels like I have less time now? But I spend only around 90 mins longer at my office job than I did at school during High School.
I will say that college definitely felt like a lot of free time. But thats an exception and of course not everyone goes to college.