The first article was interesting, and I rather enjoyed it. Well done!
My thoughts, I quit RS when I was almost 20. Age had nothing to do with it. Playing Rs is no more or less an indication of maturity then playing an other game, rather its how you manage gaming in relation to everything else in life which is a mark of maturity.
WoW actually has a similar issue, although the thing is in WoW, a lot of the player base is getting older, meaning that they don't have as much time, or set time, (Time they can schedule every week to PvP, raid, etc) as they used to. Its a problem any MMO would have to answer, how to keep the older, limited player base interested, while training up the newer generation through content that is hard enough to actually enable them to do content later on. Its a balancing act.
To Josh: I think that it is as much as testament to the "end game" of RS (There is none, everything relies around levels) as anything that botting for levels was so common. Considering the only real bragging rights, besides "skill" in PVP, or MHing, or amount of money had was in levels, the incentive to bot is and was huge. That's a game design philosophy flaw on Jagex's fault IMO. Its also why I quit RS, in part, no end game. But yes, when I played RS, I played for the personal drive, making and setting goals. That's always what keeps me interested in a game. When that dies, I quit.