Your assertion of age is way off. Most people are going to be well into adulthood by the time they've flown enough to perceive the "security" process as its own thing.
Read my comment again. The assertion I was responding to was "Do you not remember", not were you not alive.
I'm well past the minimum age for renting a car, but I would not say that I remember airport security before the TSA - because I didn't experience it enough for it to have left any impression.
I do remember a much more recent trip to a foreign country, where on the return we were just walking through an airport hallway when I realized we had just gone through the security point. That is the way to do things.
There's maybe a few month period between the birth day cutoff and the founding of the DHS.