Most kids will potty train themselves even if it's not until they are above 4 years old.
There's no age limit for diapers and a kid should be allowed to decide when to potty train and not the parents.
Kids don't need potty training.
Although parents potty train their kids they really don't need or require potty training.
Kids will eventually potty train themselves when they are ready even if they are 5 to 6 years old when they do potty train and stop wearing diapers.
Eventually most kids will decide to stop wearing diapers after age 4 to 5 years old and go potty on their own without the parents needing to try to potty train them.
Although some parents say their kid is potty trained by 18 months to 2 years old it's really the parents that are potty trained instead.
For a kid to be potty trained they must recognize the need to go pee or poop and then go to the toilet themselves without someone taking them or reminding them.
They must be able to pull their pants down and up and wipe to be able to fully potty train.
I had a kid that eventually potty trained when he was 7 years old.
I had tried before then and finally gave up and kept him in diapers and when he was 7 years old or really 7 and 1/2 he decided one day to use the toilet and then stopped wearing diapers.