I've been DMing every week now for the last few years, but I'd say the average over time would be closer to every other week. Gotta be close to 1,000 games now.
hmm... 18 years? 18 1/2. The box said 'ages 10 and up,' so my brother made me wait for two years after he got the basic boxed set. Jerk. But by the time I was 10, he had purchased AD&D 1e, and it was awesome.