Helping toddlers do what comes naturally
If you start potty training your child when he's around a year old, the process will probably take around 18 months so he'll be clean and dry in his third year. If you start when he's around two years old, the process will probably take around six months so he'll also be clean and dry in his third year.
Most children don't become developmentally capable of taking charge of their own toileting until they are around 30 months, so you've nothing to gain from an early start. You won't save yourself time or trouble because carrying a potty everywhere you go, and persuading a baby on and off it, takes much longer than just changing the nappies. You won't save much money, either, because you'll have to keep using those until he is "reliable". You won’t be more environmentally friendly by using few diapers. In case environmental issues are important for you, you can use biodegradable diapers. More seriously, you may lose his co-operation and damage his dawning self-image, too.
It's easier to get the timing right on potty training if you think ahead about what and who the process is for. It's not a question of discipline, of making a toddler sit on that potty and perform for you. It's a question of his personal independence, of helping him take charge of his own toileting needs for himself.
He cannot begin to take charge until he is physiologically able to recognize his own need to go, far enough in advance to get to the potty. If you start "training" before he can do that, you'll be relying on your own awareness of his needs rather than his own. And that means that you'll keep interfering with his play, and his sense of being his own person, by whisking him on to that potty without so much as a by-your-leave.
Some babies don't object to that which is why some parents who put infants on potties mistakenly believe that they are "trained" but whether they have met a potty in babyhood or not, most toddlers do object. And once objections begin, you're in trouble. You may be able to force or bribe your toddler to sit on a potty, but there's absolutely no way you can make him perform there.
Once your toddler recognizes his need for the potty in time to get there if he chooses, it's up to you to help him want to take this big step towards being grown up. Pressuring him to go when he doesn't want to, or to stay there when nothing comes, may still put him off.
Scolding for his frequent accidents, or too much triumph when he "succeeds", can make the whole potty-business into an issue between you.
Your two-year-old needs to know what a potty is for and where his is always. He also needs to know that big boys use potties or toilets instead of diapers and that, because you realize how big and grown-up he is getting, you would like him to do that too, and that you will help him.
Parents are sometimes so anxious to avoid toilet training pressure that they go on changing diapers and saying "it doesn't matter" when their toddlers are preschool children. And by then it will matter, not just to you but to your child's self-image as his own person.