J.B.
My husband came up with this method we call the Reset Method. Basically, when the child starts getting into something they shouldn't, we say no, or don't touch, or whatever rebuke you prefer (keep it simple, though, and possibly use the same ones over and over - kids learn by repetition) and then RESET! Move the child back to their starting position (wherever you put them down to play in the first place). It teaches them cause and effect - you do this, you get moved back to start. Also, it distracts them from what they were doing and adds some distance between them and the off-limits item. This worked like a charm for my daughter, but my son was a bit more determined. Several resets had to happen and often, he had to be removed entirely from sight of the desired object/cupboard.
He's definitely not too young to be disciplined; he's definitely capable of understanding cause and effect (I even heard of someone starting time-outs at this age - basically the reset was to the pack-n-play for a set amount of time) and he can definitely understand no - as long as it's followed by a consequence (even like just moving the hand away from the object.
You may have some hard work here at the beginning of his mobility, but if you expend the effort now, you won't have to later.
Good luck!
J.