Supports would definitely have to be 2nd tier classes aquired at lvl 30. There's no reason for a support before that. My honest opinion though would be to make supports a cross class job aquired at lvl 60, SE would even like that cause it gives people a reason to get to 60 if they are still unsure about the game or what class they want to play.

I don't see any reason why the job shouldn't be able to play the 1-30 old content though? Old content is already mind numbingly easy anyway...