I started about six years ago, so I was maybe 38, with a couple of short-form classes at a local performing arts center. Other than me, few or no other adults signed up for improv classes, so the center hasn't offered them since. In 2007 (I was 40), I found another group/class doing long-form and have been there ever since. Age-wise, I'm probably toward the middle in our group, and most of the other people started around the time I did.