At this age the best thing you can do is to baby-proof really well so that your little one has a chance to do some safe exploring without you having to say "no" all the time. Move anything that is breakable or dangerous, then give him lots of safe things to play with. (My daughter fell in love with the pots & pans and the spaghetti strainer around this age!)
When you do have to say "no", try to be gentle but firm. Physically move him away from the temptation as you say "no", and give him something else to divert his attention.
Good luck!
I did not read all the responses, so this might be a repeat. I think there is no magical age when they understand no. We have been saying it to my son for a long time (he is almost 2) and he will walk over to something that he should not touch and go to touch it and say "no" and walk away.
I definitely suggest telling him WHY you say no. As in "No pulling on the dog's tail; that hurts him". As people should do with kids of all ages, tell them why you are saying now. We find when we give him a reason, he is much happies to take the no.
babies don't understand the word no yet. i'd wait till after a year to try disciplining. you need to watch him and baby proof everything and i mean EVERYTHING.good luck. and please keep your baby safe
Our 7 month old is doing the same - crawling, pulling up, very curious. If you put her down in the middle of the floor, she will make a bee line to whatever is most dangerous. It is uncanny. We were getting frustrated because we have a 3 year old and he needs to be able to get to things, so complete babyproofing is complicated. We ended up making "baby safe zones" - a pack n play in the kitchen, a saucer in the playroom and an octagon-shaped pen in the family room. We call it her cage :) We got it at Toys R Us and it's a big enough space that she can crawl from one side to the other. We attached an activity center to it, and put safe toys inside. She tolerates if for much longer than the pack n play, and we can go about our business and play three year old toys on the outside, and she's content to watch us from in there.
I agree that he won't understand "no", but that doesn't mean you can't say "No, that can give you an owie" and redirect him. Just don't use it to discipline, because there is no such thing as discipline at that age.
And just two more things - I certainly wouldn't give a slap on the hand. Kids learn by example, so unless you want to get slapped, don't touch him. And, I laughed when I read "Crayons are for paper...". That is my mantra!
Good luck, once they become mobile it's all over! They certainly keep you on your toes :)
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!
Jean