I grew up in an environment where my parents definitely encouraged the general concept of outdoors, adventure, etc., but we didn't really do anything on that front. I maybe camped twice on cub scout trips, although one of those was in a luxurious adirondack shelter.
That said, when I was about 7 or 8, my grandmother gave me a copy of Richard Halliburton's Complete Book of Marvels (a fantastic book, although it's very, very out of print to the best of my knowledge), which had a chapter on Yosemite that stuck with me for many years- particularly the section on Half Dome and the cable route.
I finally went to Yosemite in 2010 for the first time at age 24 on a trip with my sister, and did a little bit of day hiking. Part of me wanted to hike Half Dome, but I didn't – something like *that* was obviously for better, fitter people. Not something someone like me would or could ever do. At the time, it was the right choice (I had never "hiked" beyond walking in a patch of nearby woods and was horribly out of shape), but the stories of the "climb" still stuck with me.
I went back to Yosemite in 2012 by myself, after getting off of the couch and in shape, and did the Half Dome hike. To my surprise, it wasn't that bad (still a heck of a dayhike, though) and it started to make me think about challenging myself more in the outdoors. This time, though, my admiration and envy turned to all of the backpackers coming in from the backcountry with their giant backpacks. Their trips sounded fantastic, but I was convinced that what they were doing was for experienced outdoors people- surely not something I could ever do.
Two months later, I stepped onto the trail for my first overnight. Two years later, I finished the JMT. On my monitor, I have the planning spreadsheet for my 2015 PCT thru open on my computer.
Everything I did to get into backpacking, I did in the second half of my 20s (basically the last 2 years), but I'm not sure I would have even had the spark of interest in some of these places if the stories about Yosemite hadn't caught my attention when I was 8.