Opencast has a standing policy of supporting the current version, and the previous version. In general terms, this means a roughly 1 year support cycle for any given release due to our half year major releases. Support, in this context, means development time: building fixes, applying them, and releasing those changes.
For example, as of the time of writing we currently support versions 6.x, and 5.x. Once version 7.0 releases, version 5.x will no longer be supported, but 6.x will. Questions for older releases will still be answered on list, but developer time will usually not be allocated to fixing issues on those versions any longer.