Being a moderator isn't necessarily fun
It's like being a regular member, but with the added responsibilities of dealing with spammers, dealing with help request PMs, moving topics, removing obscene content, etc...
Basically, if an admin were to make you a mod right now, you'd probably find it less fun, exciting and interesting than you think you will.
This post brought to you by someone who has never been a mod on a popular forum (although I have on a few small ones and I've administered a few, and have also read several accounts from mods).
The only real upsides of being a mod are knowing you're contributing to the community, access to mod-only forums, having your name in green, and being able to use mod edit tags
But if you do want to be one, just hang around, be a long-term regular, be helpful, follow rules etc. Given that, there's a reasonable chance that you'll be a mod eventually- mods will leave, gaps will appear, and you may be spotted as just the right candidate