It's not just age, I think: it's the fact that the stakes are higher. Every change to Python affects a lot more code that people depend on than changes to Ruby. Another result of Python being older is that people have begun to recognize (some of) the bad ideas, and can be a bit terse in their responses to the N+1th proposal something shot down N times already. A third factor (and, in my experience with #python, the primary reason large IRC channels breed meanness) is the conflict between people who want to understand the new guy's motivations and desires, try to guide him to a workable solution, and refuse to help him shoot himself in the foot, and the people who see no problem in helping them aim straight down and blast away, so to speak. In a larger community, there's less room or time for persuasion and argument in either direction.
So, yes, as a community grows it becomes less tolerant of certain things. The alternative, so far as I can tell, is for the community to fragment and waste time pursuing each faction's agenda (See Scheme for a good example). The important thing for contributors is to avoid burning out; if you've had a certain conversation a hundred times, the hundred and first can tempt one to short-temperedness quickly :) On the other hand, if being more friendly means accomodating people with screamingly bad ideas, like willy-nilly syntax changes, or ruby's "safe" (I searched Google for 'ruby safe' to see if it is really as bad as I remembered; all I found were security advisories, so I'm guessing "yes"), then I am in favor of unfriendliness.