When i try to portforward minecraft it says old near the playercount

Assuming you run the server, which version is it?

(As an example) If your Minecraft is 1.7.4 but your server was downloaded from 1.7.2, you won't be able to join the server on your client until you load 1.7.2. (Edit profile > select version > save and launch).

Keep in mind that when Minecraft is updated, the updated server will always become available for download via the official Minecraft website - http://minecraft.net/...t/download

If your server and client are both running the same version, refresh the multiplayer listing. Sometimes it is a minor error that corrects itself upon reloading. If not, try joining 'localhost' (only if you're running the server) or attempting to join the server regardless of the error to bypass the problem.