There are no member groups (that I'm aware of) that have site-based restrictions against using PMs -- not even a brand new member with 0 posts to their name. I have specifically checked the "User (Inactive)" group that Michael was a member of and he had (site) permission to send and receive PMs provided his personalized settings allowed such (see last paragraph below).
There are some limits -- particularly on younger members -- as to how *many* people you may address a single PM to (typically a single PM may be sent to no more than 5 members). A PM addressed to more than the maximum number of allowable recipients will be refused by the system.
HOWEVER, the member has the power to turn on/off Private Messaging and/or the receiving of PMs via their personal Settings console ("Settings" link can be found in upper right-hand corner of the page) for themselves. Under "General Settings" (link can be found in left-hand sidebar) you will find the controls for customizing the behavior of PMs for your account. These settings apply only to the individual member.