There is nothing wrong with an older child still wearing diapers. If he still needs them or still wants to wear them, then a diaper can be something very practical for an older child.
We have an older boy who still wears diapers, during the day and at night. For him, diapers and being changed are part of his daily routine and it looks like it will stay that way for a while. There is always protection under his pants or pajamas. So he can wet himself and everything stays dry. At night, for example, he would still wet the bed every night. Therefore, there is nothing wrong with him still wearing a diaper.
We also still have a changing table and blog about it:
https://tobischangingtable.wordpress.com/