My dad gave me a buck folder when I turned 8. I carried that knife with me from 8 until I graduated from high school, although, the later few years of high school, having a knife in my pocket would have been looked on as carrying a weapon in a lot of schools, but thankfully our little rural school wasn't that way.
I lost that knife for about three weeks in my apartment during trade school. I was sick to my stomach about it, so I bought a different knife and retired my folding buck, tucking it safely in with my other sentimental nick-knacks in an old H. Upmann Hecho in Habana era cigar box that lives on top of my dresser.
The only time you'll find me without a knife is when I absolutely can't have one, which is while flying. The rest of the time, I've always got one. For the last ten or twelve years, I've been carrying a Gerber Crucial multitool instead. It's not much bigger than a standard pocket knife, but has pliers, a phillips and flat screwdriver, knife blade and the all important pry off bottle opener. I heard they discontinued them a few years ago, so if this one craps out, I suppose I'll have to find something suitable to replace it.