Possibility to limit old content that is displayed to a new user
To do this, you probably should implement hook_node_access($node, $op, $account).

You should return:


NODE_ACCESS_ALLOW if content is new, or user have premium role
NODE_ACCESS_DENY if content is old and user does not have premium role
NODE_ACCESS_IGNORE if you do not want to control access for this content type


There are already contributed modules to sell roles, or to take payments, so this part should be easy.

Note that hook's documentation says:


  See Node access rights for a full explanation.


I strongly advise to do it.