What if we're looking at stuff from the wrong end?
Rather than finding ways of giving more experience to new characters, why don't we make it harder for older characters to function?
We could call it "Age", and when a character reached a predetermined value, it would take more and more XP to increase stats, until eventually you've no option but to retire.
Note that you still have a goal that you can strive for - there could be a table with the highest scores achieved (Or MPR or whatever). But now there's no static top ten that people feel they have no chance of getting into
Obviously there's stuff I haven't thought through (all of it), but what do people reckon?