If you haven't taken him to the dentist, then it is definitely time. (I didn't actualy take my daughter until she was nearly three, but I had already been flossing and fluoride wasn't a concern).
Start with a fluoride free toothpaste (there are tons of them out there) in order to teach him to spit and not swallow. Spitting is fun for them and teaching them to do it only at toothbrushing time is a good lesson.
YOU need to be brushing his teeth, he can start, but you need to finish.
If any of his teeth are touching, you should also be flossing.
The thing about fluoride is that you don't need a whole lot of it to have an effect. The friction of the brush is as helpful as anything and making sure his mouth is really clean before bed.