While I wasn't obese, I was overweight until the end of high school. For some reason I thought weight = 10*age and it took me a while to realize that this would be unsustainable past 20. Now I'd say I'm more fit than average (try to work out ≥4 times/week, have ran several half marathons and a marathon, decently adept at skateboarding) and people can't believe that photos of me as a child are the same person.

I'd say this is more of a boiling frog situation where I don't perceive a demarcation between life before and after getting fit.