My first "real" (i.e., non-kids) bike was a Motobecane Mirage. I bought it in about 1970 or so and had it for several years. I was kind of reckless back then and rode an awful lot. Over time, I had to replace every single component (except for some roller bearings and the seat) on that bike because of damage from accidents. Somehow I came through it mostly undamaged.
I also completely stripped and repainted it one year because the paint had been exposed to too much cold and snow and it all curled up and flaked off. I sold it to my younger brother for ten or twenty bucks but I have no idea what he did with it.
My first bike as a kid was an old narrow tire, single speed coaster brake Schwinn.