I was 10 years old or so, which means I am coming up on my 25th anniversary.
Oddly enough, most of my D&D stuff came to me somehow second hand.
I still remember when the red boxed set turned up out of nowhere. The damn thing was so confusing I was sure there were books missing (there may have been). I know the dice were missing-- I didn't own a set of "original" light blue dice until years later.
I won a copy of the 1e DMG off a friend in high school on a bet, and I found the 1e MM left lying on the playground.
Several times I got just tons of books, entire boxes, turned over to me at once. Modules constantly came to me second hand-- I still own 2 or 3 copies of all the great classics.
I don't think I actually bought a single D&D product (except dice) until I was in college.