It was a long time ago but I attended a session by IBM at an OO conference. The speaker's claim was that the half-life of programming language knowledge was 6 m

It was a long time ago but I attended a session by IBM at an OO conference. The speaker's claim was that the half-life of programming language knowledge was 6 months i.e. if not reinforced, that how fast it goes. I learned the Q array language five years ago and then didn't touch it for six months. I was surprised how little I remembered when I tried to resume.