The age that boys stop using diapers is between the ages of 2 years old to 3 years old at least during the daytime.
However some boys may still need to wear diapers at night for bed wetting until 4 to 6 years old and even up to 8 years old or sometimes longer if they have issues with wetting the bed.
Kids with autism or other development delays may not stop using diapers even in the daytime until age 5 to 8 years old and some kids may need to wear diapers all their life.
You can start potty training a boy when the boy starts showing signs of being interest in using the toilet or when they can recognize the urge to pee or poop and can get to the potty and from the potty which often occurs around age 2 to 3 years old.
Some boys may be ready to begin potty training as early as 18 months although some are not ready to potty train until 2 or even 3 years old.
The best age to potty train a boy is between the ages of 2 years old to 3 years old although some boys might be ready before then or may not be fully potty trained until 3 and 1/2 to 4 years old.
Most boys are potty trained by age 3 although some boys may not potty train until age 3 and 1/2 years to 4 years old.
Some boys are potty trained as early as 18 months of age but even when you begin potty training at 18 months the child still needs lots of help with using the toilet.
When it's all said and done even starting as early as 18 months the child is not fully potty trained and able to use the toilet independently until age 3 to 3 and 1/2 years old.
If you wait until at least 3 years old the boy will have better bladder control and be more able to get to the toilet on their own and pull their pants up and down and wipe without much or any assistance.
I've always waited until my kids were 3 before even beginning potty training and went straight to underwear without using pull ups.
Once they were 3 my kids both boys and girls all potty trained within a few weeks to a few days.
When you potty train as early as 18 months or under 2 years to 3 years old it's more the parents being trained to take the child to the toilet and remind the child to use the toilet.
If you potty train before 3 you will be dealing with lots of accidents which means in reality the child is not ready.