If the player regardless of age was able to come up with the money to pay for destiny on their own (Birthdays,Jobs,Chores) then i have no issue. Clearly they are mature enough. However i have an issue with players who were unable to acquire the money on their own or not on a special day (Birthday,Valentines,etc....). In my experience these players are the ones who act above everyone else and have trouble listening to directions and hints. These players get booted from my fireteam. There are exceptions, but if you could not afford the game on your own, chances are you are below the age of 10. Again there are exceptions, you could be a 9 year old with a greater mental age than most 21 year olds. (Yes i do ask players how they got their copy, IMO it is very telling as to how they will act in game)