All kids are different and will potty train at different ages.
There's no right age for a child to be potty trained and out of diapers.
But most kids are fully potty trained and out of diapers by age 4 at the latest.
When your child shows signs of readiness then it's time to start potty training.
If you start potty training too early it can actually take longer to get the child fully potty trained.
A child should be able to hold in his/her urine, and poop long enough to make it to the potty and recognize that they need to use the toilet.
You can start introducing your child to the toilet at around 18 months and he may or may not be interested but it's worth a try.
Your child should also be able to pull up and pull down their pants and go to the toilet on their own.
If they can't do that then they're not really ready to potty train and you should wait for awhile until the child is ready.