I'm legacy level 4 right now. The official announcement of letting people qualify for the free month via legacy level included examples of what kind of character level spreads would have enough XP between them to have legacy level 6. For one character, it was "level 50 and has spent some time doing endgame."
CCP has an actual economist on payroll to analyze EVE Online's economy and prepare detailed reports on it. Presumably you can find the reports somewhere on the game's website.