A child can begin getting disciplined around age 12 months of age because at 12 months of age you can begin reasoning with the child and they're old enough to be getting into things and doing things they shouldn't.
If they start doing something they shouldn't at age 1 then you can start telling them in a serious manner that they shouldn't be doing.
Say no to them very sternly and don't laugh otherwise they won't think you're being serious.
You can also put the child in Timeout for every minute of their age once they're 2 years of age and above which is very effective as it was used on me as a kid.
I hated Timeout and I would be good then to avoid Timeout.
Sometimes you may need to even smack the child on the hand if they're in a dangerous situation as sometimes that's all that works to get the message across.
It's not abuse if done correctly and could save your child's life.
Even spankings if done correctly works wonders to keep a child in line.