I've clicker trained my buns. I highly recommend the clickerbunny.com site - it's linked to the book that the BB store sells and has great tips that are specific to clIcker training rabbits (most sites will focus on dogs, but they can still teach you a ton about theory if you're interested).
First, most guides will tell you to "load" the clicker by clicking and treating. In my experience, this is a waste of time and you can move right onto training something simple, like standing up. Your rabbit won't understand what the clicker means at first, but by the time he's learned his first trick, he'll have a pretty good idea. I found Otto didn't *really* understand the clicker until he was learning his second trick. All of a sudden, you could see a little light bulb go off in his head as he generalized why I was clicking.
Make sure you treat every time you click. Eventually you don't need to click for every behavior and you can reinforce every other time, or every third time, but if you click, you must treat.
I would start with simple tricks and then move on to other exercises, like handling. If you try to do something uncomfortable, like touching feet, right away, the game won't be fun for your bun. If you start with easy fun things, let them learn how to learn, then try handling feet and things they will understand how the game works. My boy doesn't like to be touched or picked up, but when we're playing the clicker game (at least he thinks it's a game) he'll let me touch his feet and pick him up a couple inches from the ground - he knows that he can control when he gets a treat by playing along.
Finally, don't try to put verbal cues to tricks too soon. Wait until your rabbit is reliably offering the trick on his own, then say the cue word (or give the hand signal) right as he's starting to do it. Eventually he should learn to only do it when you request. Personally, I've found that neither of my rabbits are very responsive to cue words - they don't seem to understand that my words have meaning. One bunny is better with it than the other, but for both I've found that hand signals work best.
There is no best age for clicker training. Just jump right in! He might not have a lot of focus at first, but that will get better as he understands the game.