Yes in my opinion it should be the kids decision as to when they stop wearing and using diapers and start using the toilet.
You could introduce the toilet to the child as early as 18 months of age but if they are not interest don't push the toilet and just keep them in diapers and try when they are 2 or 3 years of age.
Some kids will decide on their own that they don't want to wear diapers anymore and are uncomfortable in diapers when they are wet or poopy and will ask for a diaper change or remove the diaper themselves.
I've had a kid I was babysitting who was 4 years old and still wearing diapers full time and one day he came to me and said he needed a diaper change.
So I changed him into a new diaper and then a few hours later when he needed to pee he said he took the diaper off himself and went to the toilet.
Some kids don't always do that though but if they are getting near 5 years old then you should force the issue of the toilet and get them out of diapers but if the child is under 4 years old or less in age and in diapers full time then don't force the issue.