I haven't been around long enough to notice trends, but I agree with Caine, that younger people are more likely to come and go from the scene as they figure out what they want, whereas those in older age brackets have probably figured out what they want by now, so they don't come and go.

As a guess, since I have absolutely no information to back this up, I would think that there are more lurkers and transients in the 18-30 age group, so even if there aren't actually more people around in the 30+ group, they are likely more active, since they've had more time to figure out what they want and are probably more certain of themselves.

As I said already, I have no idea if this is true or not, but it was an idea, and I'm being unusually talkative today, so i had to type it out.