Only 6.5/6.6 versions of the OpenSSH client can connect to this server. 6.5 is the first (and as far as I know only) ssh client that introduced chacha20 and ed2

Only 6.5/6.6 versions of the OpenSSH client can connect to this server. 6.5 is the first (and as far as I know only) ssh client that introduced chacha20 and ed25519 support.