Versions 5.3, 5.4 and 5.5 have technically reached "end of life". That means that they are no longer supported, and maybe exposed to unpatched security vulnerabilities.
Version 5.6 is still supported for critical security issues (till 31 Dec 2018).
Version 7.0 has active support until 3 Dec 2017, and security support till 3 Dec 2018
Version 7.1 has active support until 1 Dec 2018, and security support till 1 Dec 2019
For the latest details on supported versions, click here