As far as APA, there is no waiting period mandated for contact, excluding romantic contact. There is a 2 yr ethical mandate for romantic contact, but such contact is discouraged, regardless of time passed. It also depends upon whether or not the T is retired, at least in terms of logistics, because once a license is surrendered, there's no sanction to pursue. Basically, the APA urges members to give serious thought and reflection to any contact and cautions against the T initiating contact.

I don't think my T had a specific policy across the board. I'm sure he considered a former client's vulnerabilities, progress, and termination status individually. I'm pretty sure that in most cases, contact was somewhat limited, if only because of the nature of his client base: transient Univ students, so not usually long-term.