The age at which a boy should be fully potty trained is 4 and 1/2 years old at the latest.
Some kids may not fully potty train until 5 years old but by 5 years old the child should be potty trained and out of diapers during the day.
The kid cannot go to Kindergarten wearing diapers and not being potty trained unless they have some health issues.
It's okay if the child needs to wear diapers at night for bed wetting past age 5 years old.
I had to wear diapers starting at 8 years old again at night because I was wetting the bed and wore diapers until 13 years old.
I had to also wear diapers at age 8 years old to 13 years old on road trips because I would fall asleep on the road trip and wet my pants.
To be fully potty trained means that the child can get up, pull their pants and underwear down and go potty and pee or poop on their own without any help from the parents.
If a child is unable to get up, go to the toilet, pee or poop, wipe themselves and then pull their underwear or pants back up then they are not potty trained.
If you have to help the child go potty then really they are not ready as a child should be able to get to toilet and recognize they need to go on their own.
Some parents think that a child is potty trained even when they can use the toilet with help but in reality they are not.
In my opinion a child really is not old enough to be fully potty trained until at least 3 years old and I've babysat 2 year olds who were partly potty trained but they were having so many accidents and needed reminded to go to the toilet that I decided to put them in diapers when at my house.
2 year olds can use the toilet but some need help.
It's okay if a 2 year old or even 3 year old is wearing diapers and they are so young for so little time that having them in diapers for even 4 short years is not an issue.
Heck I would even change an 8 year olds diaper as I would want to keep the kid in diapers as long as possible.